It all boils down to practical matters such as panel size vs available roof space, portable vs fixed, etc , etc.
I my case a 255 w panel and an Eco-Worthy 20a MPPT was just perfect with the 5er as a portable in a twirler contraption on the ground near the trailer where we stayed for weeks at a time.
Then we got the truck camper which sometimes needs solar, so I got into swapping the big 255 panel back and forth which was a PITA.
So then last year Can Tire had another of their sales on 100w panels for $200 so I got one. (Now of course they are flogging them for $175 on sale) Then just before solar season got going for us, a guy down the road was selling two 100w panels for $100 each, (made in India in 2015! very nice) so I grabbed them. Now I had three 100w panels, so I planned to sell my Can Tire one for what I paid for it and go with the other two and bought the Tracer 20 amper so I could play with it to try the two 12s in series, which the Eco-W can't do.
But I never did sell the third 100w panel and still have the 255w and the Eco-W. Also I have a Solar 30 PWM I got a while back.
So this year I first tried the Solar 30 PWM with the three 100s and got 3 x 6.1 amps as expected = 18.3 amps. Then I tried out the Tracer but it only got me 17 -18 amps too, being limited to 260w. Never saw 20 amps on the thing no matter what.
I suspect I could get a little more than 18.3 with MPPT if I had the 30a Tracer instead of the 20a when the batts are in the low 13s but I will never know! I need to have a garage sale and get rid of half this solar stuff! :( Oh well.
Point being, it is not about theory, it is about what happens, and once you buy it you own it! :)
My twirler, modified to hold three 100s from just the single 255 last year. Easy wiring swap at the back to go parallel or series.
