Our shop was primarily a GM/Ford house before I came to work for them.Owners purchased a couple of Genysis tools with smart cables and that covered 75% of what they did.Some bi-directional,no program capabilites.They felt they were opening themselves up to unwanted problems by "reflashing" or downloading software upgrades.Coming from a Dealer background,they saw Ford's wonderful diagnostic hardware and said "no thanks".
I have been working on German cars since 1985 and they REALLY did things differently.Bosch had lots of tools out there and as the dealerships did away with those machines,money was all it took for us to get our hands on them.The Bosch "Hammer" for Porsche was one example.A few people started reverse eng. these tools,and they actually got better than dealer level equip..User friendly might be a better term.
Right now I use VCDS for all my Audi/VW work.Loaded on a netbook,I can use it while going down the road or in a stall.The guys at Ross-Tech upgrade this tool about every 4-6 months to de-bug and add new features.I can run a readiness test after repairing emissions faults without leaving my stall.No more 2 trip drive cycles,keeping the car overnight.I know its fixed.The only thing I have not been able to do with it is program keys.More to do with VW's security than anything else.
I have other 1 auto line scan tools that were purchased as they became dealer cast offs.All work extremely well for a specific time frame of certain model years.There are modules you can only access thru these tools.But,as new scanners come on to the market,they are able to read more indepth than before.Depending on what you mostly work on,is it more important to excell in say ford diesel diagnosis.Or do you want to be able to do a little of everything,leaving some holes because the software developers have not gotten around to that yet?
I would ask the various tool vendors "who do you know that has tool X in the area?".See if you can borrow a demo.When Snap On found out I was looking for coverage of more Euro cars,they had a Regional guy come out and give me a seminar on their tool.The Euro coverage at that time was sparse.If they sense a sale,most of them will stumble all over trying to convince you that theirs is best.Make them prove it.Set up a demo car and have them over to diagnose it.Even NAPA has a scan tool division.But do not buy until you are convinced that this will help YOU in your business.