We've done two trips w/Magic Bands now...the last one was last month, and we did request (and get) an old-style KTTW card...
We're in the 10%...we had hours' worth of problems on both trips with the new technology (the first trip was to SSR in November; the second to VGF in February)...
Most of the problems were with FP+...had no issues getting into the parks and while it took some finagling to get in to our villa at GFV w/the magic bands, they always did work...and we had the KTTW cards when we ran out of patience w/the "positioning of the wrist" issues to get the bands to work...
The problems w/FP+ were huge, time-consuming and very annoying...but ultimately resolved. The CMs at the GFV were particularly nice & tried very hard to be helpful (I also tried (but failed) to resolve the issues, over the course of multiple hours and phone calls prior to leaving home)--
As far as my experience goes, if you have a straightforward reservation with everything you're doing done thru Disney, you should be fine--one of our problems was w/the
UT park hopper my friend had--I could NOT link it to My Disney Experience (and thus could not get her any FP+ reservations)--as it turned out the CMs at GFV couldn't get it to link either...after several hours, they just issued my friend a new ticket, which they linked and copied my FP+ reservations to--so it worked out, but took all of our check-in day--we got the new stuff that night. If, however, you have any "unusual things," there may be issues. E.g., for my upcoming trip in June, I have 2 nights on points, one night on cash and 2 nights on points, plus an AP that expires mid-trip (the plan is to renew while I'm there). So, I will either have to plan on lots of time to sort things out, or just do without ... my choice is to do without--I'm not planning on using FPes at all this upcoming trip...no way I'm gonna spend all that time, particularly while I'm on site, trying to make the "buggy" system work!
For me, that's ok...I go to Disney a lot and a trip where I ride few (maybe no?) rides isn't a huge problem for me...
But for me, the issue is "My Disney Experience" and FP+...I use a different email address for "commercial" purposes and Disney has my two email addresses completely (and seemingly irrevocably) confused...makes using MDE really painful. So my "solution" is to just not use it.
I very much dislike this new system. But there appears to be little or no choice about using it. Either you do without "the goodies" it provides when it works, or you put up with the (many) bugs (unless you have a very simple trip plan)...
As for charging...I decided under no circumstances will I ever put my credit card information "on file" (or on MDE or on a magic band) for any reason...the convenience is so not worth having my credit card connected to a system with so many bugs and flaws...
That said, when the magic bands work, they are quite convenient (if you don't find something on your wrist annoying)...I particularly liked it when coming back in from a swim or hike...mine did come off, once, altho I noticed it right away and refastened it and it was fine...and it is probably no more of a risk to lose a band than it is to lose a KTTW card...
As for staying at Disney while going to US/IOA--I did that last year and it worked out really well...my friends did book a room at a US hotel, and the room was nowhere near as nice as our OKW villa...the "early access" was nice (they put me on the room w/them, altho I went back to OKW to sleep), but the days we went we didn't need it (even for Harry Potter)...and there's much to be said for not paying for a hotel room when you have points to use! Of course, getting to US from Disney is an issue if you don't have a car...it's a pricey cab ride, or a time-consuming (reserving/getting there) bus ride...still, at over $200/night for the US hotel room, those points villas at Disney are mighty appealing!