Of the ribbon mics coming out of China, there are long motor ribbon mics, like the Apex 205, short motor ribbon mics, like the RSM4 and dual ribbon mics, like the CAD Trion ribbon mic. Different brands of ribbon microphones coming out of Chinese factories are variations of the body built around one of these three ribbon motors.
All have a potential for ribbon sag. It is not hard to fix, but a careful and adventurous DIY spirit is required.
They seem to all have the same transformer. Some people like the sound imparted via passing the signal through the stock transformer, some people prefer to swap it out with something else like a Cinemag ribbon mic transformer.
There is a number of layers of mesh, wire and silk inside the mic body head basket to protect the ribbon. Many people choose to remove some of that stuff and feel like the sound produced is more clear as a result.
Many people actually replace the entire ribbon with thinner material and they feel like the mic then produces a louder, more responsive signal with a greater level of clarity.
My DIY opinion on these various ribbon mics is look for the cheapest version and go for it, with the plan to upgrade the mic. I have two RSM5 mics and two APEX 205 mics. The longer ribbon motor mics tend to be a little brighter and the shorter ones tend to be a little darker. Generally speaking.
I LOVE, LOVE, LOVE ribbon mics on rhythm electric guitar. Especially coupled with a condenser. Love them. Sometimes on vocals depending upon what type of result I am seeking. I have used them as drum OH, but it depends upon the set up and what other mics I am using to capture the sound of the kit---used for drum OH, I am assuming I want to capture an over-all kit sound while controlling cymbal wash, which they do very well.
They can require a great deal of gain, but as someone else mentioned, there are things like the Triton Fethead that assist in providing enough clean gain for the mics. I personally have learned to prefer clean gain on my ribbon mics, as they are providing a healthy dose of color already. Yes, ribbon mics are very distinctive and very colorful. I would not want a ribbon mic as my only microphone, but I would certainly want at least one as a part of any studio microphone collection I would ever own.