IMHO...this is just my opinion and that's about all it's worth...
Over the years I've had many electric motors on my kayaks...
The first was the simplest... a "side mount" MinKota or Motor Guide trolling motor attached with the regular hand twist knobs on an aluminum L bracket that was bolted to the kayak deck just behind the seat well and in front of the rear tank well. A 'heavy' deep cycle Group 24 12V battery was installed in the tank well and it worked pretty well and lasted a long time, especially if you were judicious with your speed and use. This set-up was installed on a OK Malibu II and a Cobra F&D.
During my last few years with the OK Fishing Team they came out with the Torque kayak with the electric motor system...I loved it and with my accelerating arthritis in my hands and wrists it was just what I needed..! But it still used the heavy batteries.
Since I've been on the Hobie fishing team I've seen the Torqueedo motor system which is great... but pretty it's expensive for the regular guy and kind of complicated.
I've built a Motor Guide system that used the Hobie cassette for the Mirage Drive (it worked great...although it was a little tricky to get it through the Mirage hole) and I've tried the Water Snake motor...it was inexpensive, small and light...but it didn't last long. Both systems used the Big Heavy group 24 12V batteries.
I've been using the Bixpy Jet Motor and their lithium battery system for the last year or so and it's been great
Bixpy has both a rear mount and a Mirage Drive mount...I tried the rear mount which allows the use of the Mirage drive peddles...I prefer this mount when in fresh water lakes and salt water areas without any Eel Grass or Kelp...but when out in open salt water areas I really like to be able to get to the motor to clear the kelp and grass....it's almost impossible to clear that stuff when the motor is mounted 8' or 10' behind you.
Good Luck...PM me if you need more info.