HI Nick,
The grey ones are clones of the Roland system 100
The black one are clones of the Moog system 55
The silver ones are clones of the arp 2500
I have a few of the Roland and Moog ones. The build quality is fantastic and having used them, my experience is not on par with the anti - Behringer backlash you tend to hear from I guess I'll call those peeople purists. Each to there own though, the prices are fantastic so there are no complaints from me on that front. I pair my Behringer filter with the Intellijel rubicon 2 as there are 3 inputs on each filter and 3 modulation sources per filter as well as two outs per filter. The only thing I'd say is the hpf settings are a bit severe for my taste and really thin out the sound so I tend to not use those but as I understand they are advertised as 'faithful to the original' remakes.
regards