We always recommend radio modules for anything but the highest volume new products. It's easy to cost-reduce one out (worst case, you just build the module yourself), it just takes a bit of cash flow to pay for it. And if your product isn't earning any money, then you have bigger problems than radio cost....

Anyone doing "small" (<1k) runs will be using bluetooth modules, but unfortunately the EMC cert is for the unit as a whole, at least in the EU. Which makes sense technically as the construction of the whole unit matters - conducted emissions through the power supply, for example. It does make it expensive and annoying to do small production electronics, which is why all the stuff you might see is "modules" from aliexpress.

<1k units runs tends to get a pass from EU authorities anyway.

This has no legal status, it's just that hardly anything actually gets checked. Conformity is self-reported, so either you have to lie about conformity and hope that you probably won't see any enforcement, or do the work.

You can see how well the "regulation but no enforcement" regime is working by picking up any disposable vape from the street and looking for the WEEE "do not bin" symbol. It will probably be there.

Germany is one of those more likely to check. A few years ago, our first few units delivered to Germany were stopped at customs and sent back for no CE mark (how they got sent that way is another matter). So we Made SureTM all units for EU had it.

Then Germany rejected again because the "CE" was obviously in the wrong style, on a generic sticker (I'd warned, but been told "It'll be /fine/."). And German Customs said our slip directing customers to our site for setup and operating instructions was insufficient. This time, they held our units until we sent satisfactory documentation.

Finally, we were able to send, but with after a warning from Customs that a third error would result in permanent bannage and seizure at the border of anything we sent to Germany.

Yes and no and it doesn't matter :)

Broadly and simplified:

Adding a bluetooth module means that, not only is the device no longer "electrically equivalent" (which means you are re-certing), but you have gone from "unintentional radiator" to "intentional", which means you have a different and/or additional set of standards.

A pre-certified module (as in, it has modular approval) under FCC means you do not have to test the "intentional radiator" part the module PROVIDED you exactly follow the instructions of the module supplier AND you don't do anything "stupid".

Under CE, pre-certified module isn't a thing. It will certainly help you pass from a technical standpoint, but doesn't really let you "short-cut" the testing and paper work.

Hope that makes sense and gives a rough idea.

edit Apologies for rehashing what others have already said. I should have refreshed.

> How about using a pre certified bluetooth module

The device is what gets certified, not its parts.