racing takes place on the road. racing requires going fast on the road. IMO, training on the road is ALWAYS best when feasible. I think rhythm on the bike is super important, and that doesnt come from riding the trainer. learning how to keep power up on downhills and manage efforts in that situation is necessary, because, well, racing takes place on the road.
try them on the road, I'll bet even though you get there in a different way, your AP will be within a few watts of an effort on the trainer, and you'll have what is a more realistic representation of the efforts necessary for competing in races.
that being said, if you cant do them on the road because of time considerations or whatever, I'm pretty sure 2x20s on the trainer are better than 0x20s.