A few notes shortly after getting the mics:
First off the picture shows a 1/8" jack for the microphones; the one I received uses a mini-XLR (3-pin) connection, similar to, BUT DIFFERENT than a Shure TA4F connector. So, one should be able to find replacement microphones.
Secondly, the description specifies 200 channels; it appears to be 100 channels (0-99) for each mic (so 2 x 100 = 200?). The A side seems to be 510.10MHz ~ 534.85MHz in steps of 0.25MHz. The B side seems to be 545.10MHz ~ 569.85MHz, also in steps of 0.25MHz. Thus the two sides won't conflict with each other.
In terms of frequency and spill, I will note that the microphones seem right on the frequency they claim to use; using approximately 200~300kHz of bandwidth (i.e. ~125kHz on either side of the specified frequency). This explains the 0.25MHz steps. However, there seems to be a side channel at ~1.7 MHz higher than the specified frequency, and using about 100kHz of bandwidth. So, in other words, When configured for 532.6MHz, the signal was very strong between 532.5~532.7Mhz and also right at 534.3MHz This side channel signal is about 30dB below the primary channel. I don't know what it's used for, but you should be aware of it.
Although the manual states 590~890MHz, the actual frequencies supported are 510~570MHz, so they are legal to use in the US. The provided antennas support 510~560MHz, so this confirms that.
The transmitters are not fixed A or B, I was able to get the transmitters to sync with either side, even though each side has a different frequency range.
The transmitters are all plastic; the battery door is held with very small plastic tabs. The back clip slides off (pushing down) with a firm push; no need to actually push the button to release it. The microphone heads are by no means small, they measure about 14mm in diameter and 28mm long, and come with a foam windscreen and clip.
The manual indicates the transmitter power button is under the battery cover, along with a set button. This is not the case; there is a power switch on the top of the receiver and no set button. There is an IR window under the battery cover.
Syncing is easy via IR transmitter; so, configuration is pretty easy, even though the frequency itself is not shown while selecting the channel. The receiver shows the frequency normally, but you configure via a channel. The transmitter shows both the channel and frequency along with the battery level, and what appears to be transmitter power. The receiver indicates RF and audio levels, with a mute indicator. Battery is only shown on the transmitter.
The units are 1RU in height, you might have to remove the feet. While there are screws which look as though they might make it easier to rack mount, I think you'd need to fabricate your own brackets. The units also don't appear to have a way to connect them to each other to double them up in a single rack space; you might need to use a shelf.
The power requirements are 12V DC, 500mA.
I give it 5 stars for the price, but subtract one start due to the side channel that might cause interference.

Excellent microphone! Durable easy to use and sounds great.

Not the prettiest lavalier mic you've seen but it works very well in our church sanctuary.