Having run both Night Fears and Neutral Grounds, with a mix of people familiar with the system and people completely new to the game, I can say that they work very well as one-shot convention games/game demos.  Especially in Neutral Grounds, the questions they have you ask players in the beginning even give people a small taste of building the setting/their characters.

So I'll add my anecdotal evidence to the reviews.

It depends on what you want to do.  Stunts are better for some things, while Powers are the best at the small subset of things they do.  It's possible to make a perfectly effective character by taking only Stunts or only Powers, but plenty of players mix and match. 

My 8(+2) Refresh Pure Mortal seems to stack up perfectly well against the 10 Refresh Wizard and 10 Refresh Shapeshifter in our tabletop game, and I've seen some pretty amazing pure mortal builds on these forums.  That said, my mortal is specialized in social combat, and there aren't many Powers that effect that, so I can't speak to whether or not my experience is typical.

Would tagging for effect allow you to have that one attack inflict damage on both parties, if it hits?

Were I GMing, and you asked me that question, I'd allow you to treat that one "Human Bowling Ball" attack as a spray attack against those two targets.  You'd have to split your shifts on the attack between the two of them, and both of them would get a defense roll (the enemy you're throwing could manage to land safely with Athletics, and the one you're aiming for could get out of the way.)

Like all invokes/tags for effect, though, it's very much at your GM's discretion.

I think the DFRPG system could definitely handle C:tL.  I really love Changeling the Lost, but I haven't played it in a long time because FATE mechanics are just so much better.  If you want any help converting the system over, let me know!  I'd be happy to lend a hand.

I think Pledges could probably be handled with aspects - when you make a Pledge, all parties to the Pledge now have that Pledge as an aspect on them.  That Pledge could then be invoked (to represent boons granted, glamour gained, etc.) or compelled (to represent favors/tasks/alliances you've agreed to) just like any other aspects.  Breaking a Pledge would probably give all other parties to that Pledge a free tag on the Oathbreaker's Pledge aspect.

For Contracts, it really depends on how you want to do it.  Perhaps pick some appropriate stat and have it determine how many dots of Contracts someone can have, and have another stat determine what the highest level of Contract you can use is?  Maybe charge Refresh?

Talecrafting actually works remarkably well with DFRPG - when you're Talecrafting, you're basically just declaring an aspect on the scene and then invoking it for effect.

I don't remember as much about the Hedgespinning system, but it could probably be handled like a thaumaturgy ritual in that you would need to spend time gathering the right ingredients etc beforehand.  Only you'd likely be rolling Crafts instead of magic.

Invoking any aspect (including consequences) always nets you a +2, no more and no less.  The 2, 4, and 6 is how much stress you remove by taking different consequence levels.

I think what Harry is doing mechanically is invoking his consequences and other aspects that were placed on him to fuel his magic.  Maybe he even placed some of them himself - I could see rolling his Conviction to place RIGHTEOUS FURY on himself, as an example.

I think the question that concerns our group is: Can a player be forced to "Choose?" Can a player be forced to make their character non-playable? An NPC? Even if it is part of a story, like with Changelings...

The whole vibe from DF RPG and FATE system in general tells me... Probably not. If a player doesn't want their character to become an NPC, then they can make all the right choices to prevent that from happening by the rules as written.

Changelings are Scions. So, that's what brought the question up. Changelings have an explicit Choice to make when playing the game. Remain mortal and have some nifty powers or... become Fae and get some more nifty powers. The rules say that the former is a PC and the latter is an NPC. We're wondering if other Scions have drawback and, even in the case of Changelings, can that Choice be forced upon you?

I would say that the Choice can't be forced, with a caveat.  Narratively, if the character keeps drawing on their nonhuman heritage and developing more and more powers, they're going to get to the point where they effectively make their Choice and become an NPC.  This isn't forced - this is due to actions the character took, the Choice the character made to keep drawing on and developing those powers despite knowing where that path would lead.  At any point up until they become an NPC, though, they can make the opposite Choice and become a pure mortal.

Mechanically, a GM can compel a PC to take actions that lead to the character making their Choice, but the player can refuse the compels as long as they have Fate Points to spare.  And, as others have said, it's bad form for a GM to compel a character to become an NPC.

The caveat is this: In the case of Changelings, there is one known way to force someone's Choice - arrange for them to receive the mantle of a faerie queen/mother/lady.  However, to do this, you would need to A) Be able to kill one of the most powerful beings of faerie and B) Arrange it so that the Changeling was the closest possible vessel for the mantle.  So...it's extremely unlikely to come up in play.

This is pure speculation on my part, but it's possible other scions might be forced into their Choice the same way, depending on how gods' mantles work.  In the highly unlikely event that a god is killed, would the god's mantle then settle on his nearest scion, effectively making their Choice for them?

I think the book itself addresses this in a sidebar.  Basically, they admit that declarations are much easier than assessments and explain that the reason they're so much easier is because they encourage the players to fill in details of the scene rather than always asking the GM to make up aspects.

Those are awesome looking! 

My group just uses plain old poker chips...I always grab the white ones because my character is affiliated with the White Court.