Good/bad commercial car systems.
I'm from a small UK HHO company and so not really much interest to you guys over the pond, but would agree with most of what's been said.
When I look at some of the systems being sold by some other companies I do realise that they are so out of line with what we have found actually works, and I do worry that HHO car systems are getting badly misrepresented. That can be bad for the genuine developers who are doing things correctly.
The truth can't be hidden forever, though, and I think that the posted results of various peoples MPG gains show doubters that this can actually work, and will keep this movement going.
Anyway, to help give you some pointers, a good efficient cell (5+MMW) , limited maximum current draw of around 20A for most vehicles and 2 sq inches of plate area for every amp draw per plate , a bubbler to prevent any backflash and clean the output before it gets to the engine, intake into the air filter box in case of any overspill, and careful installation to avoid heat and snagging of cables/pipes etc should be a high priority.
Price should be representative of a fair cost of the kit, with a fair rate for time to install carefully, preferably by someone with some experience of installing.
I hope this is some help.- Buster-http://www.wix.com/emissionsbusters/emissionsbusters