JMO disclaimer
The mash and boil is a nice little compact, reasonably priced countertop system.
Drawbacks imo would be that it is slightly underpowered and undersized for full volume mashes, so a sparge is required for full five gallon batches.
With a little experience it is very easy to hit an accurate strike and mash temp and then wrap the unit in a beach towel or blanket to keep a reasonable steady mash temp.
If you want or enjoy playing with pumps and upgrading the temp control, knock yourself out.
The beer produced by either learning to use the unit within its limitations, or by upgrading it with pump and control will be darn near identical.
I view the simplicity of the M+B as a plus, and wouldn't change it a bit, but would just perfect a technique for the system.