Assuming the use of a patch bay, balanced to unbalanced isn't a big deal if you wire everything properly.
True enough however, never assume. Many of the home recording types (like me) don't use patchbays and it can be a problem.
I found, even with properly wired TS to TRS/XLR cables as detailed on FMRs website, I had noticable signal loss (More than 3dB). When I put it through a hum eliminiator to balance, the signal loss became less pronounced (about 1dB), but I had to get a hum eliminator and throw it in the chain.
So if you have to buy a patch bay or build/buy special cables and or hum eliminators/DIs to balance the thing in your network, then it becomes a less price attractive piece since you now have to factor in the cost of additional cables and boxes to get it to work right
I've never found the RNC "slow to react" for any use needed here. I will concede that the metering is less than stellar in Super Nice mode and suspect that this is what you're referring to.
Yes super nice mode is unpredictable and difficult to guage. Running the signal through some properly calibrated VU Meters I found I was getting gain reduction long before the meters registered anything. It also has a very soft knee and the manual makes no bones about that. I just found it difficult to use and a lot of transients were not caught
There's no need to concede

, this is just my subjective opinion and to quote Douglas Adams, "I'd far rather be happy than right any day"
What you call "bland," most would call transparent, a trait many happen to appreciate even if you don't.
Absolutely and I did also say that my point of view was entirely subjective and the whole opinion should be based on whatever sound you are individually looking for. If transparent is what you want then the RNC is a "really Nice" option. I'm not bashing it.
The RNC is a great compressor to learn about using a hardware compressor properly on, it's well made and the price (assuming you already have some equipment in situ to do the balancing for you) is very attractive.
In the end however it wasn't for me because of the "Balancing Act" involved and I was looking for a more textured sound
YMMV