The only way I would use the new M250 was if I was very limited on space. It will be cheaper to go with the M215 the M215 will really tops out at 225 watts so they mate very well with 250 watt panels.
The M250 really does top out @250 watts.
They both use the same trunk cable. You still have to ground the racks/panel frames .
I had sales people telling me the M215 topped out at 215 watts when I was buying them this is just not true at all.
Look at the image at the bottom on this page.
http://ecorenovator.org/forum/solar-...r-array-2.html