my beef with the crucial m4 is the slow write speeds compared to the competitors. and the price seems too low i.e you pay for better quality.
The price is low because Micron (of which Crucial is the consumer arm of) is one of the top NAND manufacturers in the world. They have a joint venture with Intel and produce arguably the best NAND in the world. The Marvell Controller on the M4 is also very mature and likely doesn't cost them much.
The M4 may have slower write speeds but for client workloads it is at least 75% about the reads. The read speeds on the M4 are great especially when you take into account that it does not slow down if you deal with a lot of incompressible data like the Sandforce drives do.
The Samsung is generally about the same speed, has better writes and arguable deals with high workloads not as well as the M4.