Not fired both but I do have both a F&D FW149 (6.5 and used on .243 and .270) and a UTS131 (.30 cal being used on a .270), the latter with a Hausken M15 to M18 adapter - great quality machining!
Both are so light that despite being front mounted silencers, I simple don't notice that they are on the end of the rifles. There are quieter silencers out there, but I think F&D have got it right in terms of sound reduction for weight. For stalking, IMHO they are perfect. On the range for long strings for load development, zeroing etc, I use Wildcat Evo mods and then slip on the F&D for the final zero to take out the small offset in POI. If its the MD35 Mini which comes in at 130g, it seems a direct equivalent of the UTS131 but I prefer the "cleaner" shapes of the F&D but that aesthetics.