He's not anywhere near the first to have sold the DA off for another engine. Brillelli is another that has been used to successfully replace and improve performance over a DA. It's always for the same reason. The DL may be an improvement on the DA design rather than a direct copy. Suffice to say that the differences between the DL and the DA are enough to eliminate the induction problems commonly associated with the DA.

There are quite a few good engines out there. The "best" one is the one that performs the best for you, and quite often it will not be the most popluar one. Unless you have been willing to spend a lot of money to obtain various 50cc engines the only one most will have any direect knowledge of will be with the one they own. Those that buy numerous engines, work on them for hire, or work with them for a living, have the opportunity to experience a much broader product base and develop a pretty good feel for which is better than another.