From using regular ear plugs, my experience is that you really need to get them in there quite far. Also, I find that the disposable ones are really basically single use. After they've compressed and expanded I find they don't seem to work as well on subsequent uses. So, taking them out and putting them back in is something I would try to minimize. Maybe they've improved in the meantime?
The molded plugs to me do feel a lot like a properly inserted ear plug and with the filters in, there should be no gaps. It should be a very snug fit. I've got 10db, 17db and 26db filters. The 17db filters are the sweet spot for me, but it's nice to have options.
With (high power) hearing aids, it's reasonably easy to know if you have a gap in the mold: I'll get a feedback loop (annoying noise, naturally) if one is loose or a poor fit. Interestingly, for the past few molds (a 4-6 year life per pair these days) the left ear definitely has more of a problem with feedback loops when my jaw is opened wide (i.e. eating) - the shape evidently varies more with this movement than the right ear does.
The molded plugs to me do feel a lot like a properly inserted ear plug and with the filters in, there should be no gaps. It should be a very snug fit. I've got 10db, 17db and 26db filters. The 17db filters are the sweet spot for me, but it's nice to have options.