I and a couple of other people have got a luminary from them, from personal experience, I think they are good, far cheaper than Arcadia and OK not as good but I think an sensible compromise between cost and quality. You are probably paying a bit for the name with Arcadia ones, although they are the best if you have the cash spare.
Note with that one that the tubes dont reach all the way along the luminary, which might be a pain. Mine also only has one plug so its all or nothing, although it seems this one has two, although the ad seems to imply it has just one, worth checking. I think the Arcadia 4 series have two plugs so you can have a more gradual increase in the light intensity.
The auction will obviously go up, check out a 'buy it now' one for an idea of the likely max price, although I did get my 3x24w 2ft one for around 20quid less than a 'buy it now' one so well worth watching.
You'll also have to change the bulbs, but James saved us some cash there with his cheapo T5 tube test and article. 8x Arcadia plant pros is gonna be around Â£160, which makes these less competitive.
Hope that helps
EDIT - Why does it say the tubes are 35w? Don't think you can get 35w T5 tubes!
I did think exactly that but you can have 4 or 8 lights on at any time. If...and it's a big IF i did get something like this, i'd have 4 tubes on for most of the day and maybe boost it up to 8 for a couple of hours of "midday sun"