sfx2000
10
spoken like a non-technical person 
Honestly, it’s not that simple…
It does - it also supports 20MHz and 40MHz channels in 2.4GHz
40MHz channels do have some caveats, and here, it takes a fair understanding of 11n and the rules in play - it’s not automatic that one can force Wide Channels - at a driver level, it’ll do 20/40, and fallback if the local radio environment says it’s just not possible because of nearby WLAN’s.
Actually, it does not, 802.11n was designed to be backward compatible with 802.11b/g - and it is - disabling older legacy actually introduces issues around greenfield, mixed, and legacy - and for many, it takes things down a more complicated code path.
Again - it takes deep familiarity with the 802.11 specs in general, and knowledge of the rules at hand, just like 20/40.
Pretty much anything with a Atheros, Realtek, or Intel chipset run fine - Intel is not USB obviously, but common in chromebooks and windows laptops.
best!