I did a smash Oktoberfest- ish with it. Wasn’t bad wasn’t great but I put that more on my yeast and hops choices. Red x is a blend of grains I believe so it’s not a simple flavor.
As stated above, it can be used up to 100%.
I made a red IPA with it at almost 100% and it came out great!
It is most similar to a dark Munich, but maybe a bit more malty.
I just kegged my annual batch of Red Rye which normally features Red X. My LHBS stopped carrying it so I subbed in Munich II and cara ruby. In my experience, Red X is way too rich to use @ 100% however it works well as a portion of the base and possibly a specialty malt. My prior versions split pilsner and red x 1:1 and I really liked my results. I think it could do well at higher percentages but I would recommend adjusting water and hops accordingly to balance it. The one time I used it at 100% it was too overpowering.
Early indications from my current batch is that it is a very different batch from previous versions using red x. The color has gone from a great red to a medium amber at the same calculated SRM and the grain profile is very different as well.