Yes you send your supplied EVSE to EVSEUpgrade and they'll make it a Level 2 capable of supplying 20a. If you need more than 20a for speed(say 27.5) then I'd purchase a 30a EVSE, like one of the ClipperCreek models you linked. Now if you can live with 20a then I suppose you wouldn't need the ClipperCreek, also if you just needed the 30a ClipperCreek and were OK carrying around a simple L1 120v EVSE then you wouldn't need to spend the money upgrading your stock EVSE.
Personally I like carrying around a EVSE where I had the option to use 240v and I also like the option to charge at 27.5a at home, for quick turn around, although truthfully most of the time the 20a provided by my EVSEUpgraded EVSE works just fine
Personally I like carrying around a EVSE where I had the option to use 240v and I also like the option to charge at 27.5a at home, for quick turn around, although truthfully most of the time the 20a provided by my EVSEUpgraded EVSE works just fine