an off branch of Shure that I know of is JTS and they have a JTS 57 model which sounds just as good as the Shure one. even though it is cheaper,
if thats any help?
check out the shure website, that might help.
The PG57 has a frequency response of 50Hz to 15KHz, versus the SM57 with a frequency response of 40Hz to 15Khz.
To me, the PG series mics seem a bit less durable.. it seems like an SM57 could take a fall from a mic stand a lot better than a PG57 could. Most of the PG57's include an on-off switch as well. (The SM57 can be had with an on-off switch, but it is not the norm from what I've seen).
I'd say if you're just using it for a home studio type setting and are on a budget, a PG series mic would be fine.. but if you're planning on gigging with it (or just aren't careful with your gear) I'd say save the extra $30-40 and get an SM series mic.
The '57 is a classic. Everyone should have at least 2.
They're darn-near indestructable, and can be used to record anything well, not perfectly, but for guitars, it's the go-to mic, regardless of how high end the studio. Why? Because it WORKS!!
a 58 is basically a 57 with the spike in the 4k frequency. The 57 is uni-directional, where as the 58 is a bit less uni-directional to account for a singer not holding the mic directly in front of his/her mouth.