1. The cover can be definitely combined with the sucker. Ie they can be used between the suction and the vials are (tested with Avent Teesauger and Naturnah sucker!).
And
2. The cover are 100% leak-proof.
A Super solution so.
As Note: The caps must be used with the Avent logo to bottle out (bulge protrudes into the bottle) back and not for suckers. Then the lid fit that is also between the teat and bottle are tight.
So we are fully satisfied with the product. Packaging and shipping of course also as always 1A (because Amazon directly).