= FAIL
The auto bed leveling readings just didn't seem right. So I did a test. I ran g29. Then added a magnet in the far right corner. Ran G29. Removed the magnet. Ran G29. Here are my results:
(pay attention to column 4, row 3)
1st Run: no magnet:
SENDING:G29
Bilinear Leveling Grid:
0 1 2 3 4
0 +0.795 +0.362 +0.227 +0.553 +1.102
1 +0.438 +0.102 +0.012 +0.250 +0.765
2 +0.025 -0.370 -0.442 -0.205 +0.305
3 -0.573 -0.952 -1.102 -0.843 -0.365
2nd Run: with magnet:
SENDING:G29
Bilinear Leveling Grid:
0 1 2 3 4
0 +0.827 +0.370 +0.227 +0.555 +1.125
1 +0.462 +0.105 -0.005 +0.235 +0.775
2 +0.032 -0.382 -0.462 -0.220 +0.312
3 -0.578 -0.963 -1.132 -0.860 -0.645
3rd Run: no magnet:
SENDING:G29
Bilinear Leveling Grid:
0 1 2 3 4
0 +0.838 +0.365 +0.220 +0.553 +1.135
1 +0.467 +0.107 -0.005 +0.232 +0.780
2 +0.035 -0.382 -0.462 -0.223 +0.307
3 -0.575 -0.963 -1.132 -0.857 -0.360
So magnetic flex plate is out.
I'm not running the MKS Gen L v2.0 board in my printer. Mine died. I have a BTT SKR 1.4 Turbo. It's very similar to the MKS Gen L.
You can still hook up the BLTouch. There's a servo port and you can use the z-axis limit switch port to trigger it. I think, though, after looking at the board that the "AUX 1/2" would also work. The z-axis limit switch is the easier way to go but I want to say I remember that there is an advantage to using another pin.
TeachingTech did a video on this board in the Ender 3.
Also, here's the docs on the board: https://github.com/makerbase-mks/Datasheet/blob/master/English%20datasheet/MKS%20Gen_L%20DataSheet.pdf
If you need firmware compiled with it setup just let me know. I don't think this is too hard to do.