It can be a bit of a pain to mix. You can see when it has covered all the pellets when they go paler. I've never tried verm x but I think it is a preventative more than treatment. I treat with flubenvet every six months.
Are you from UK? Flubenvet is the wormer of choice here. I've never used the pellets but I have used the powder you mix with pellets. There is a 7 day withdraw for meat, no withdrawal for eggs.