@awise1961 I've heard the Backert Labs Rhythm and their Rhumba in a number of systems, including my own about 5years ago. Caveat is that I know the guys from Backert and consider them friends, although we haven't stayed in touch much since I relocated out of their area 4 years ago.
What I can you is that our local audio club had about 80 members. Backert demoed for the group. Over a couple of year period, more members bought Backert preamps than any other component by any brand. It seemed like every time a new buyer hosted a gathering and people listened, somebody else decided to get one. This includes members with a wide variety of ss, tube, every type of speaker, etc. Those preamps were beating all kinds of preamps, many at higher prices.
They are natural in timbre and don't need to be paired only with warmer or cooler gear. They are super quiet and notes start and stop on a dime, giving them their name. Andy, their president has worked as a professional musician; they know what music sounds like and they listen to ridiculous numbers of options for every part to optimize SQ. If I could afford to, I'd get one now.
They are a relatively new company, but Bob Backert has been in the biz for decades. They've got some unique tech(read up on their patented power supply), and are a tube roller's dream. I just wish they'd make a model that's truly balanced, vs. just having XLR outputs. Just my humble experience, Cheers,
Spencer