I love this mic in full disclosure. It's designed to be hung from the amp with a piece of duct tape right up on the grill direct on.
That being said, that's going to give you an extremely specific sound that you may or may not like. I like to blend this with some other mics when the amp works.
It's not as tough as an SM57
but it works and it'll take a bit of a beating. For live situations, a piece of gaffters tape is a lot less to carry than an extra stand plus it's harder to bump into. Less stage clutter...
In the studio, the difference between this mic and an SM57
is like the difference between a humbucker and a single coil. This is more scooped sounding but for some amps, that's just what the doctor ordered.
It's not as cheap as some, it's cheaper than others. I also like to use this on Baritone Saxophone and banjo. As far as Banjo goes, it works great with the high impact attacks but has the nuance for the decay.
If you already have an SM57
and are looking for an affordable option to blend it with on guitars, it's worth buying, just make sure there's a return policy because it may not be your cup of tea.