The Sennheiser e609 is a great dynamic mic for recording guitar amps both in a studio and live setting, as I have used it in both. I put it right up against the speaker and it comes out great most of the time (of course depending on the amp, guitar, player, etc).
I've had this mic for about 3 or 4 years now and although I don't use it as much as I used to but it is still a great option for recording guitar amps and I love having it in my arensel. Compared to a Shure SM57, it has a pretty similar sound to me, and I do prefer the Sennheiser 421 on guitar amps over the e609. However, for the price this is a great mic to have around. Although they say it is also great on toms, I could never get the right sound with this over a tom tom and it was a bit hard to place on it. Overall I would definitely recommend this mic to someone who is interested in having a new option for guitar amps, but I would also recommend having a Shure SM57 and a Sennheiser 421 to compare it with.