The modern one I have the most experience with is Wessel-Werk's EBK 360. I like it, but there's a lot of room for improvement. 
Pros:
				
			Pros:
- Cleans well and reliably - single pass is almost always enough
 - Motor is more than powerful enough
 - Belt wears pretty slowly (lasts at least as long as the roller brush)
 - Wide cleaning path (~12")
 - No hair tangling issues
 - Standard IEC C7 power connector
 
- Lighting isn't terrible, but it easily could be much better
 - The mechanism that locks the neck upright is relatively weak
 - Replacing the roller brush includes replacing its bearings and pulley gear
- The pulley gear is plastic and wears at a similar rate as the bristles. Would rather see a metal pulley and more targeted replacement options.
 
 - Motor bearings used to be high-quality sealed ones from... Schaeffler, but it seems they downgraded to shielded off-brand bearings.
 - The wand retention mechanism is a leaf spring button style (the button being on the wand). It doesn't fail quickly, but it does weaken over time.
 
- I think it's about time to switch over to a brushless motor, and possibly even direct-drive.
 - Better control circuitry would be nice. Right now it's just a simple rocker switch. This is cheaper and a bit easier to replace, but I'd rather see the rocker switch control a relay for longer intervals between needing any replacements. Cost different would be minimal.
- I know many people don't like soft starting, but it would take some wear off the drive components (and switch/relay).
 
 - It would be good to have a smaller gap between the cleaning path and the outer edge of the cleaning head on the non-driven side. It's not too bad how it currently is, but there's definitely room for improvement.
 - Old height adjustment pedal was a bit 'mushy' to use. It's been redesigned, but I haven't had a chance to use the new one yet.