The 70-300 f/4-f/5.6 is a cheap and relatively underrated lens, soft in the corners but capable enough. The 80-210 is an older design, but seems to have some reasonable net reviews, all saying 'for the price...'
Compared to your L glass, though, it doesn't compare at all, but you probably knew that already.. Still, this costs less than an official canon lens collar, so for cheap thrills, it's got to be worth a punt!