I didn;t use reptomin, but instead used a different brand (cannot for the life of me remember it, but it had a green label) when I was first keeping newts.
My axolotl I fed on axolotl pellets given to me by the lab I adopted him from, and I continued to buy and use these. I bought the green label pellets when I bought my first chinese fire bellied newts and they ate them well and I founf the brand was highly nutritious. I did not remove the pellets after they had gone soggy as I found that within 12 hours the newts ate them all anyway and there was rarely any mess left over.
However, since expanding my collection so dramatically I have come to rely upon frozen bloodworm and worms as they are easier for me to source in bulk than the newt pellets. I also find it easier to transition to frozen bloodworm rather than pellets from the bbs and daphnia I feed my larvae. I have not tried most of my current species on the pellets, but am considering making another search of the internet for a bulk supplier after reading your post. In addition, the variety of sizes of newt pellets seem to be less than I require for the variety of newts I keep (with the exception of axolotl pellets, which appear to be available in a variety of sizes).
Edit: the brand I used was JurassiDiet, just found it online!