I'd guess it would be a bad buy. Rockworth is B&Q own brand so far as I am aware so will likely be equivalent to any bargain basement stuff you can find on eBay.
What do you want from a TIG? For me I'm not an expert TIG welder so HF start rather than lift start is an essential feature. Other than that the cheap inverters tend to work reasonably well, though might not last past the guarantee. Guarantee from someone reputable is worthwhile so you don't need to buy new ones more than once a year.