I will admit that I personally have a Reliance panelboard with an interlock between the main and positions 2&4 in my own residence.
Hence, I think it is code compliant.
I hesitate to tell this story, but ....
A few years ago, I had the deadfront off for testing during a storm and was negligent in putting it back on before going out for work with the generator running. While I was out, the utility returned and my wife, feeling very capable, took it upon herself to perform the transfer that she has watched me do many times. After opening the generator breaker, she went to operate the 200A main, and after having difficulty getting enough leverage to close the handle, she put 2 fingers on the top of the main breaker which happened to be the incoming energized conductors. After about 30 minutes of tingly and numbness, we are lucky that there are no lasting "physical" deficiencies.
Clearly it may have been worse if she closed the main without opening the generator, or just the shock hazard from the main from my own negligence, but I still think it is a code compliant installation.