The perennial cheap mic combo offered by that big music gear store
Here it goes: The cubic zirconia in the rough of these two mics is the MXL 991. It's a small diaphragm condenser microphone.
It's on the bright side of things. For comparison, we recorded tracks with the 991 and several other mics ranging in price from $19 to $1,000. How did the MXL 991 fare? Not bad at all. The MXL 991 is a cardiod pattern mic. We liked it in two places: Acoustic guitar and over a drum kit.
It's too bright for my tastes to use it in a solo instrument setting but in the context of multiple tracks I thought I wouldn't mind using an MXL 991. My favorite acoustic guitar mics range in price from $200 to $300 and I even got one that I use a lot that costs $800, which is the Blue Dragonfly. In the context of the MXL 990 and 991 package deal, the MXL 991 costs about $50. One of my friends who owns a commercial recording studio uses the 991 and owns several of them. I now know why. Yes, it doesn't as good as my fave $800 go to acoustic guitar mic but it's pretty good nonetheless. And, if someone craters the 991 while here on a session, then I'm only out $50 rather than $800. The MXL 991 possesses a little sizzle that you don't get with the Blue Dragonfly, which possesses a complex high end that normally only comes in more expensive microphones. Still, the 991's sizzle comes across as a smidge musical and it's not grating (on acoustic guitar anyway).
On a session, my friend, Steve Beckett, used the MXL 991 over a drum kit. Interestingly, he also used the Blue Dragonfly (yes, it's a great mic for this use as well). He liked the 991 on the floor tom side of the kit.
The MXL 990 is a small diaphragm cardiod pattern condenser as is the 991 but the 990 is in a different body in a side address configuration. The 990 did not do much for me on most things. Steve Beckett pointed out he liked it on toms. I'd heard from Harvey Gerst about his son Alex Gerst using the 990 on toms at recording sessions at Indian Trail Studios in Sanger, Texas. Steve played me some of his tracks with the MXL 990 on toms. I listened. I found myself reassessing my distrust of low cost mics. Yes, it did one thing that did not suck.
The Bottom Line: I would limit the use of the "cubic zirconia" 991 to acoustic guitar and to over a drum kit. I would limit the use of the "it did one thing that did not suck" 990 to toms. Street price for the pair including carrying case is $99 approximately at that big music gear store.