Curtis,
Brian is spot on...as usual! You could easily go without it, but I've found it to be a great piece of gear...worth every penny, and more.
My RV is VFR, but I do a fair amount of X-C. The AP-74 is a great button-smashing saver in both local and X-C ops because the value knob is configurable for multiple tasks.
On mine:
turn the knob without pushing it...move the heading (or track) bug
push once then turn, adjust the altitude bug
push twice then turn, set the altimeter
You also get the AP on/off and mode buttons all right there.
To be fair, getting to the AP menu on the 10A isn't that bad, but the AP-74 gives you really quick and easy access. 'Course, I'm a bit lazy!
Not trying to sell ya, just wouldn't want you to be sorry ya missed it. Might fit under your XPNDR (horizontal install) or to the left of your steam (vertical install).
Either way, you'll like the AP! Have fun!
Cheers,
Bob