m2 ssd drive question

[themaniac]

first question how good are they compared to normal sata ssd's (i think thats what the normal ssd's use)

second question i was on pcpartpicker and it said 

 

 

The motherboard M.2 slot #0 shares bandwidth with a SATA Express port. When the M.2 slot is populated, one SATA Express port is disabled.

could you explain that as simple as you can

third question are they good as boot drives

the one i'm looking at is http://pcpartpicker.com/part/crucial-internal-hard-drive-ct120m500ssd4 

[TheSLSAMG]

When you use an M.2 drive, the SATA Express port is disabled. It is that literal. And they are fine drives.

[themaniac]

When you use an M.2 drive, the SATA Express port is disabled. It is that literal. And they are fine drives.

ok thanks