Not an expert, but the last BIG-IP LTM I saw a couple of months ago didn't support TLS acceleration without a dedicated hardware module (and the accompanying license); this would usually mean upgrading to a more expensive model.

Plain old TLS termination isn't license-limited as far as I know.

EDIT: to answer your question, yes, you could probably do it with haproxy, but the added value in these appliances is iRules (TCL hooks for all network events, you could augment request processing etc) and vendor support.