the 100 and 160 has the pump, internal to the body.
the 150 is external mounted.
i have been running the BM 160 since september, not a single problem.
regarding taking the pump out, its really simple 4 nylon threaded screws. you can take skimmer out, and service really quickly.
i used to be in plastics business, have to say, quite robust design, and excellent fit and finish.
mines came with the needle wheel, have not tried mesh mod, or other types of impellers. i heard rumors, there was another style available.
c