I use the Floormac and the Envirodri Gen 4.
Both are great machines but....
As Steve says the plastic casing on the Gen is weak - it's quietly deteriorating and if I can get another 6 months out of it I will be pleased - I bought it 2nd hand though it was pretty much new so it will have lasted about 18 months. Not great. In my opinion it is a domestic machine to be used a few times a year in the home, not daily on every crap filled carpet under the sun. I find the brushes are a pain to change somethimes as well with the hexagonal pin going through the middle of them struggling to fit back through after removal (will make sense to Envirodri users). Despite these issues it is a fantastic machine for lifting pile and agitation.
I bought the Floormac second hand again - I was only just starting out so most of my kit was pre-used. In the last few weeks it has developed a problem whereby there is about an 8th of an inch too much play when it is oscillating causing too much vibration through the handle and way too much noise. Not sure if this is the same issue as Jamie described. That said, it is still usable and is a great machine and very versatile. I use it for agitation - the black brush for wool, the orange brush for everything else, and for bonnetting with the driveplate and 17" pads. If anything it is a little light but hey, you can't have everything. You can also agitate stairs with it.
I suspect I will plump for a TM4 when the Envirodri carks it, depending on what they quote me to mend it, and a new Floormac when the one I have finally gives up the ghost (unless a 2nd hand one comes up in the meantime - what a skinflingt I am)
Chris