There are 3 models; M3 $1000, M5 $1600 and M7 $2500. They function the same, difference is in the electronics; how many different programs, Bluetooth connectivity etc. Main difference between the M3 and M5 is that the M3 has a manual difficulty level control, like a rotating speed shifter on a bike. With the M5 it's all electronic. I thought I would've been fine with the M3. But found that on the used market there were only M5 machines. I reasoned it's their more popular seller. Got my M5 off Craigslist for $850, like new and assembled (it ships disassembled). I was pretty sure that I'd be able to find it used as many aspirational fitness machines end up being tossed.
I think I was lucky to discover this machine. I was at Dick's store pondering on whether I should buy weights, and a Bowflex M3 was right there along with treadmills and elliptical machines. It looked interesting so I tried it. After one minute on the machine I was considering buying it. Then tried the elliptical machines to make sure I wasn't missing out on something even better. I found my movement on the elliptical machines felt unnatural. That's when I realized how good the Bowflex Max is. It has a fan and blows air out the bottom sides depending how fast you're going, an additional detail that makes you feel like you're achieving something. And it takes up little space.