Well, I have had the Flex system on my Guider II for a while now and so far it is performing as you would want it to.
I am using PEI on my flex plates.
I also went to a Micros Swiss all metal hot end set up since I do a lot of ABS printing. Really wish the Guider II had a variable speed parts cooling fan!
Got everything dialed in using Flashprint and PLA.
Then switch to ABS and adjusted.
Switched over to S3D and now am doing 250X250mm ABS prints and boy being able to pull the plate to get the ABS to release is heaven for this printer.
Main thing to note.
My Guider II had a pretty warped glass plate so look for that.
I went to my local glass place and got replacement glass that they said would stay good and flat. So far it has worked well.
So make sure your glass is perfectly flat, especially while heated.
Apparently Chinese made tempered glass is notorious for being warped or curved. This is fine for most applications except our printer beds!