In contrast to the M4 there are no problems here. The disc is delivered with the latest firmware (MU03) and works from the start reliably. The performance is very good and is a "conventional" SSD in every way. The price-performance ratio is excellent.
The m4 had 128GB capacity, the M500 comes with 120GB. I suppose that this is due to an internal memory allocation that is used for the replacement of defective sectors and is due to an even higher reliability.
Compared to mSATA SSD's from other manufacturers a mature product is obtained here at a bargain price. Strong buy recommendation!