I have a hand crank for my Singer 221 featherweight. It's a lot of fun to use and comes in handy if I want to sew somewhere where there's not access to electricity.
The only problem is that adding the handcrank requires a little bit of fiddling with the handwheel that then makes it not able to be used as an electric powered machine. When I want to use it without the hand crank I have to spend 15 or 20 minutes removing the handcrank and re-aligning a couple of parts in the handwheel. Don't know if that would be true of your machine or not.
As far as guiding the fabric goes, I find that because handcranking is much slower than using electricity so it's not difficult to keep fabric properly aligned with my left hand while cranking with my right. I also have only used the handcrank when pieces smaller quilt blocks, I've never used it for actually putting a whole quilt top together--don't know if I'd have the patience to do that in slo-mo LOL