Just don't imagine for 2 secs that, having obtained your TW endorsement in either of these, you could jump straight into a Pitts or an Extra (or even a Tiger Moth for that matter).. They merely herald the start of learning to fly all over again.
I didn't say that you could 'jump straight into' anything. Personally, I haven't jumped straight into any new TW type without training.
Home builts can be used commercially these days?
They certainly can, the rule goes along the lines of can't be used for licence issue training but can be used for ratings, endorsements and FA's