If you notice with universal IEMs tips and insertion depth can really effect the bass you hear because your changing how good the seal is, better the seal better the bass. What you get with a custom is pretty much as "perfect seal" so bass should be very good. However I don't know how bass wise it will compare to some extreme bass IEMs in the price range such as the Hippo VB. I am also talking about the single dynamic which seems to have more bass than the BA models.
As for isolation it superb going by what I heard when both impressions in which Phil said is very much what CIEMs will isolate like. However that is what the full ones isolate like and I guess they will isolate more than the smaller ones. As for sizes of shells they should all be of amazing comfort being that these are custom milder to your ears. Hope this helps and if Project who has tried different shell sizes and models want to correct anything I write, feel free to as my CE"s are still on the way!