If I'm not mistaken, that JC Whitney unit is the same one that I bought from Jeepers and Creepers. See http://www.jeepersandcreepers.com/gear/pages/equus.htm

Note that J&C sells it for $20 less than JCW, AND they include free shipping.

As for the quality and functionality of the unit, it's doing just fine for me. I bought it when my dealer couldn't fix a check engine light after two tries, and my warranty was about to expire. (I had planned on buying one anyway, as I wasn't about to let the dealer service department into my wallet when the warranty ran out.) When I hooked it up, it came back with a proprietary trouble code that wasn't in the OBDII code reader's manual. Apparently, this issue is commonplace, as many/most vehicle manufacturers have codes that go beyond the set required by the OBDII specification.

Fortunately, I had already purchased a subscription to AllData DIY. ($25 for the first year, $15 per year after that, updated regularly including TSBs -- a good complement to the UK Haynes manual for my US-spec S70; see http://www.alldatadiy.com/) AllData has tables of the all of the diagnostics codes, including a cross-reference between the proprietary ones that my tester displays and Volvo's VADIS system, so I was able to confirm that my intermittent, recurring check engine light was caused by the same code that the dealer had attempted to fix twice previously. Alldata also told me that the usual causes for this code -- P1171, or 261A in the VADIS system -- included a faulty MAF sensor, intake or exhaust leaks, incorrect oil level(!) or contaminated oil(!). Got me about the oil issues, but I did have a thorough look around the engine compartment for loose vacuum hoses. None found. Back to the dealer.

When I got it back the third time, the service desk dweeb told me that they found a vacuum hose that had popped off and that they fixed that, reset the check engine light, and that it shouldn't happen again. OK -- they probably know the vacuum hoses on this car better than I do; maybe I missed something.

Wrong! The light was back on within a few hundred miles; same code found. Apparently, some of this dealer's mechanics like to reset check engine lights without actually fixing problems. BTW, the dealer is Red Bank Volvo, in Red Bank, NJ.

This time, I spoke with the dealer's shop foreman and told him that I wanted the MAF sensor replaced, and he agreed that this was the appropriate fix for this code. He also stated that he couldn't imagine why this had not been done previously. While the desk dweeb was listenning in, I told them both that I'd like a phone call if they come up with any different diagnosis than replacing the MAF sensor. They agreed, and I picked up my car later that day.

It's been about 800 miles since that last (ever!) trip to Red Bank Volvo. The car has run flawlessly since then, so it's obvious that the new MAF sensor solved the problem. (The code would, before this fix, show up within a few dozen miles of driving.) It's amazing to me that a moderately competent backyard mechanic with a $140 scan tool and internet access can do a much better job of fixing problems than a dealer with a dozen professional mechanics and Volvo's $10K diagnostics computer.

Bottom line is that I now consider an OBDII code reader to be a necessity for backyard mechanics with newer Volvos. Just don't stop there -- you'll need some more information than just the manual that comes with the tool. That manual will explain all of the standard OBDII codes, but for the manufacturer-specific extentions to the OBDII spec, AllData proved to be a life-saver. The two make a very powerful addition to the backyard mechanic's toolkit.