IMO it would depend on what you do. If well-rounded libraries and a good IDE would make you far more productive than a free or less expensive product, then it i

IMO it would depend on what you do. If well-rounded libraries and a good IDE would make you far more productive than a free or less expensive product, then it is probably worth the admission price. We use a proprietary Prolog interpreter (SICStus), but it comes with very good support and it has some advantages over open source interpreters that matter to us. Plus they provide continuing support/maintenance for their previous major version.