All depends on what your future plans are with the machine and what kind of power you want out of it.
If all your gonna do is a slip-on exhaust and want the cheapest solution for getting a non lean condition then a dobeck fuel controller would be a good choice.
If your planning on more mods then a slip-on exhaust and want a more accurate and dual cylinder fuel control, then either a fuel monster or power commander will be a good choice.
Slip-on's are more of a personal preference, 2 pipes that have been proven to provide the most gains are HMF and Muzzy. Big Gun EXO is one of the nicest looking systems on the outlanders and aren't overly loud, SPI are nice looking system and sound great with a moderate sound and not obnoxious, LTE have a unique sound but are loud and need a quiet core to make long rides more pleasant.
Lots of choices for slip-on's which is awesome.
And if you want a race car sound then NPP has some nice loud pipes View attachment 27077