Also figure out what type of work your aiming for... Are you doing planning on marketing towards commercial or residiential and do you think you'll be cleaning rat nasties, moderatly soiled, a good mix?
The RX-20's strong points are that it can restore a heavily soiled carpet with less effort than a wand alone, you can make more passes per minutes than a wand and the power head scrubs... another advantage is you can add a pad driver and turn it into a rotary machine for post padding or prescrubbing if need be. And though with limited success you can also use it for Hard surface cleaning with another head.. its pretty versatile.
The down sides are it can overwet the carpet if you are not careful, it can blast open a problem area on carpet such as weak seams, or pulled rows on a berber, its heavier to pull in than a wand, its hard to edge with it. And all of the add on attachments are pretty $$.
Now if you want the ease of a rotary but don't need the brute force of the
RX20, you also have the rotary
drimaster, which sometimes gets underated too often.
Rotary Dimaster benefits: you still make more passes over an area than a wand, clear viewing window so you can see what your taking out. Its lighter so its easier to grab off the truck. The unit provides high flow cleaning with a 1.5 gpm at 300 psi, and even in the hands of a novice, its hard to overwet the carpet. Like the RX it will make a long extraction time alot less strenuous. And it still restores the pile quite well. need to hit a little harder up the pressure to 400, and still no overwetting issues.
Downsides: Its a little slower than the RX. Its more at home on a residiential cutpile than it is on a berber.. (yet it does suprisingly well on commercial carpet). You need to clean out the top flow through windown often, and keep the bottom clean up.
I'd also suggest a rotovac 360i but don't have any experience with it.
Just laying out some options for you.