The MXL 603S is a small diaphragm condenser microphone for using in the recording studio. It's just about as cheap as a condenser microphone that you're going to find, and it actually sounds halfway decent. There is also a modification of this microphone that is possible where you can basically transform it into a Royer microphone. There are kits that are sold by Royer that are from Mojave Audio. I have used a modded 603 as well, but I'll focus on the stock 603S here in this review, just know that it's a good option if you are handy. The stock 603S has a 30 Hz to 20 kHz frequency range and it's a strictly cardioid mic.
While overall the sound of the MXL 603S isn't the greatest, when you keep in mind it's ridiculously cheap price, it's not such a bad deal. If you are just getting your home studio off the ground, it would be a pretty good choice for a small diaphragm condenser if you're looking to spend the least amount possible. It's fine for acoustic guitar and a set of them would probably sound somewhat decent over a drum kit. Professionals certainly shouldn't expect much from the stock 603S, but may want to pick up a pair if you think you'd be able to do a mod with the kit issued by Royer. Beyond that, pros will definitely not want to be using these as they aren't as detailed a sound as you'd get with a nice condenser. They'll do a okay job for demos in your small home studio, but aren't anything to write home about on the grander scheme of microphones. You wouldn't think that people would expect much from a $100 condenser mic, but just to cover all the bases here. I'd check it out for your small project studio or if you're a professional who is interested in doing the modification, otherwise I don't think you'd have much business with the MXL 603S.