@Mimouille: your description of the different approaches to taking impressions is fairly accurate, but your characterization of how they are used (1=acrylic, 2=silicone, 3=fitear) is not. For instance, Sensaphonics products are all silicone with a very deep fit, but the third process you describe is how Dr. Santucci instructs his customers when doing their impressions.
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If the procedure can be done properly as a DIY project, there is no reason not to do so if so inclined. I understand the reasons some do not want to try it themselves, but it isn't neurosurgery. And there are numerous horror stories of audiologists charging over $100 for a procedure that, at the most, should cost no more than $40.
1. The key phrase is "done properly." I am suggesting that a DIY approach is, by definition, not proper. This is not just about getting a fit and saving a few bucks, but about safety and hearing health.
2. If you think spending an extra $50 or $60 for professional services is a "horror story," imagine how you would feel about permanent ear damage. Is it neurosurgery? Obviously not, and no one is claiming that it is. But it is not trivial, and there are definite risks.