Neither of those welders are TIG welders. MIG welders can be great for aluminium, but not really so much for the kinds of things we as auto enthusiasts tend to weld (piping, brackets, thin stuff etc...). I would just look for an entry level TIG from a major brand, which will probably be used for your kind of price range (check craigslist). A lincoln square wave or miller diversion series TIG would probably be some good ones to look out for, but I can't say I've used either personally.
Other option is to get a more basic welder, like the ones you listed, but you might end up doing the fabbing/tacking at home and bringing it somewhere that does welding to finish the welds if you want good quality welds.