I've grown Kestrel quite often. It is a reliable cropper and doesn't seem to get bothered by slugs. You can dig them as 2nd earlies, or leave them to grow a bit more and make an early main crop.
It is very good in clay soil. When I first got my plot and the soil was not so great, Kestrel would always perform, no matter what. My soil is a bit better now, so I've branched off into other varieties. I'd grow them again though.