XS++ is neither more stable nor faster than SET lite.
SET lite is the litte brother of SE Tool 3. The_laser released it when free flashing soft appeared to advertise SET3.
One step ahead? Have you seen DB2020 patching in XS++ yet? :p
The_laser used to release new taks in SET lite whenever someone released a free soft that supports tasks that were only available on SET3 before (for example DB2020 support, or the DB2020 patching lately).
The big advantage of XS++ is the new FSX mode since v3 and the easy handling. It's much easier for beginners to understand.