Out of curiosity, how much film are you talking about and in what formats?
Hema seems perfectly adequate for 135, but do they accept 120 E6? In any case, all the film is sent out to a large commercial lab. For me here in NL it goes to Tilburg, but I have no idea if that handles Belgian jobs too. The results have been fine, though I only use half a dozen rolls per year and choose 'process-only'. From the reactions of the assistants in the shop, when they hand back the packages and I show them what is inside, they don't seem to get much E6 per week!
The old days, when closely controlled dip-and-dunk Q-Lab E6 processing was widely available, are gone. Many local shops/labs will either send the film out to a larger lab, or process it in a small developing-tank. In the latter case there can be no effective control of the process and one will not be sure of consistency from batch to batch, or lab to lab. On the other hand, these days there is perhaps less of a requirement to have perfectly consistent E6 as it is rarely the origin of a tightly controlled imaging chain.
If your batch of film is in formats handled by Hema (10x8" transparencies are certainly out of scope!) then send a test roll or two, with a couple of weeks between them, and go from there. Their large volume, relatively speaking, and process-controlled lab will be more consistent than a hand tank.