Sig 213 is not worth the money with the problems it has, it could've been so good, with the form factor and looks, but the chip is very buggy, I don't use temp control, so can't comment on that part, but when 1st installed batteries, wouldn't work, battery meter was all over the place, worked properly when reinstalled a 2nd time though. Also the mod misfires, and seems a very common complaint with it too, which really wouldn't both me if it cost $30, but it doesn't though.
I do not have a kayfun monster, but the airflow on the Merlin is widely adjustable for lung hits or MTL, even had a reducer pin for the build deck, so can reduce the air flow for MTL vaping, has awesome deck and is really easy to work on, I have liked it so much, within 24 hours of having it, I went and ordered 2 more, and is rare for me to have more than 1 of the same tank.