..rainbow sounds like a gimmic...
Perhaps "rainbow" is a gimmick. However, "rainbow" is not a reticle. Rainbow is a pallet. I thought "rainbow" was just another of the "psychedelic" pallets until I happened to use it in the RAIN. Then I had the double realization that it worked well in the RAIN and I realized why it was called RAIN !!!
With the RAIN pallet I was able to see cows at 400yds I could not see with black hot or white hot. The frequency of the need is small in my area, but if I could have 5 pallets RAIN would be among them. (Black Hot, White Hot, Red Hot, Sepia would be the other four)
However, as TLM says, even if provided you may always choose not to use them !!!
... thermal reticles leave a lot to be desired ...
I agree that fancy reticles are not needed for most of the hunting done by LSB members ... a dot or cross hair is sufficient. These days I am able to hit the thumb to hand sized rats I stalk with one shot by holding up or down an inch or so at 70yds or less. The hard part then is just making sure I guess the distance correctly.
However, if I would buy one of the high end 3x or above thermal scopes I would expect to have some real reticles. The Zeus 75mm 3x (640, 30) which I have now has none such. So holding 20-40 inches for wind at 500yds is a guessing game, which can be done accurately under target shooting conditions, but would be much tougher under hunting conditions. Hence, if I would buy one of those types of thermals, I would expect to have some useful reticles.
The Pulsar XD50 I recently got does have some useful reticles. Such as the M50 or M52. These are not designed for the MIL system I use. But I have been cranking the arithmetic converting the Lithuanian (I guess) cm and MOA system over to mils and it is useable. The PIP feature is probably mandatory for optimal use of these reticles which are otherwise too tiny to use with the MKIEB I have been equiped with. Perhaps Lithuanians mostly hunt elephants at 1500yds ... that would at least explain these reticles !!!
They are useful for smaller critters at smaller distances. But one must crank the arithmetic and use the PIP feature to optimize their use.