The Ultimate 1541 would suit me fine, but it's too expensive for me. Not sure it's worth the price.
The Ultimate 1541 is indeed the ultimate floppy emulator solution for the C64 which supports fast loaders and you get a freezer, RUE and cart emulator as bonus.
A HxC in a 1581 drive does not offer all the features and compatibility (a 1581 is not compatible with 1541 floppy (images) and 1541 fast loaders usually don't work on the 1581) as the 1541 Ultimate.
In my opinion the 1541 Ultimate is certainly worth its price.
As far as I know the 1541 & 1571 do not have a standard shugart floppy mechanism, so using the HxC with these drives will be impossible.