I have owned a Serpa holster for a 1911 since before there were public concerns about them. Now that the concerns have become widespread, I have carefully observed my own use of this holster, and I have also watched other people use them. I think that the key factor is the size of hand and length of fingers relative to the specific holster.
When I use my Serpa holster, my finger is never curved, and as the draw continues, my finger ends up extended along the side of the frame, just where it should be. So for my hand, the Serpa holster is conducive to a safe draw where my finger never comes close to entering the trigger guard. However, I have watched other people use a Serpa holster where they need to curve their finger to release the latch, and their finger ends up in a position where it could potentially move towards the trigger.
So overall, I believe that some people can use some Serpa holsters safely, since the latch lines up very well for their hands. I also think that the overall design is poor, since it does put some people's fingers in a bad position. For people whose hand shape does not line up well with these holsters, I think there is a real equipment problem. So better equipment, not just training, is the correct solution.
When I talk to newer shooters about holsters, I tell them not to consider Serpa holsters. There is no reason for someone who is not already used to them to try them out. The market is full of better solutions. For people who already own one, I tell them to carefully and critically observe their hand position. For some of them, the Serpa holsters may be acceptable for some purposes.