The CEM rebranded units I have reviewed have been a bit of a mixed bag.
The Extech unit I had was probably the best in terms of build quality, but the wireless comms failed on it. In fairness Extech support tried to resolve but never managed to.
The DiLog unit was pretty bad build quality, evidence of quite poor rework. The insulation test had excessive short-circuit current with respect to IEC requirements. Never any response out of DiLog, I even approached CEM about the unit and had no response.
The RSPro unit was the worst in terms of build quality, mostly in terms of rework that seems to have been carried out. I have never approached RS with regard to the issues.
It some respects it is a real shame as the CEM units do seem to have a good set of features, some of them are a bit unusual but very useful for me and that is what attracts me to them. I think if you get a unit that goes straight through production, it seems to be a better build, it is when it has to go for rework that the standards drop.
Another CEM rebranded RSPro unit I am just looking at seems to be a really good build and there are no quality issues with it.
If you are happy with the Biltema and it suits your needs, then that is what matters the most.
Kind regards