While the SM58 may be the industry standard and the "go-to" choice for many musicians, the Beta 58A is a considerable step up in both quality and sound.
Starting with the design, the shape and size is identical to the SM58, but the addition of a hardened grille vastly improves durability. While an SM58 grille can be dented with a simple roll off a chair, the Beta grille can handle much tougher abuse. Indeed, as well as four Beta 58As, I also own one of the original Beta 58s from the mid 1990s - to this day, despite years of use, the grille is completely dent free!
Shure make considerable claims about the hypercardioid nature of the Beta 58A, and how it can help reduce feedback (providing monitors are placed correctly, of course!). While the pickup certainly isn't as narrow as something like an Audix OM7, I feel it strikes a good balance. It's certainly tighter than an SM58 and certainly offers greater isolation form other sound sources on stage, but it's wide enough that it allows a performer to run around the stage, coming back to the mic without needing to be precisely in front of it. Of course, this is also useful in applications where a user of the mic might be inexperienced in mic technique. All of this means the Beta 58A is useful in a huge variety of situations, and doesn't irritate musicians (like an OM7 sometimes can!) with an extremely narrow pickup, while still offering isolation and good feedback rejection.
In terms of sound quality, the versatility of the mic continues. Keeping the clear, tight and punchy mid-range that the SM58 is known for, the Beta has a top-end boost that's definitely noticeable, adding a good deal extra clarity to vocals. The low mids around 250Hz are also a lot less muddy, and I find myself not needing that much EQ for most voices. It could be said that the mid-range is perhaps not the smoothest around, and some feel the top end sounds slightly artificially boosted (it is a dynamic, keep in mind!) - so if you're looking for something a little fuller and smoother, you'll need to make the jump to a condenser like the Beta 87 or Sennheiser E865. That said the Beta 58A sounds good on most voices and with most genres, and there's a a reason it's the mic I keep most of in stock!
I have gigged with this microphone many times and it has always been great! The increased sensitivity of the sm58 beta compared to the sm58 is great for vocalists with quieter voices, and the more focused directionality of the sm58 beta is good for reducing feedback, providing it is positioned correctly (ie. not pointed straight at guitar amp etc). I would definitely recommend this vocal microphone :]