MD421 is a great mic, you'll love it!
The fact is most "sound men" suck. Most of them aren't sound men at all, give a guy a Behringer mixer and a couple of SM 57's and he calls himself a soundman. When I see a "soundman" micing my bass with a D112, I know he's not a good sound guy before I play a note. Go sit in the audience at a local music club and listen to how bad the sound is most of the time. I can usually tell which instrument the soundman plays in just a few minutes. If the kick drum is louder than the vocals, he's a drummer. If you can't hear the bass or vocals very well, he's probably a guitarist.
The truth is for every hundred gigs you play, you may get good sound 25 times if you're lucky, maybe more if you're WELL established and playing the best venues in your area, but if you are doing that you've payed your dues by playing the s***ty clubs where the stage has only one monitor mix with guitar blaring through it at ear-splitting levels time and time again to get where you are today. When someone else is running sound I try not to worry about it and just play my best, because in the end, that's all you can do. Telling them what you want and how you want it to sound is a double edged sword; If the sound guy has no skills, no ear, and no appreciation for how all instuments should sound and how to construct a mix, it's like telling an idiot how to build a helicopter- it ain't gonna fly no matter what you tell him! On the other hand, as a sound guy myself, there is nothing more frustrating than a parade of people comming up to you and telling you how to do your job!
Mic or DI, I wouldn't worry about it. If the sound man has skill and talent, he can make Radio Shack gear sound great and you'll be happy with the sound. If he's a hack you can arm him with an assortment of the best mics, preamps, processors, speakers and mixing equipment money can buy and your sound is still gonna blow! Not much you can do about it either way. By telling him you want a mic, or you want a DI the only thing you are doing is ruining the slim chance of having good sound by pissing off the soundman!!!!!!!
My two cents.