Numista is great! I like, and have used several times, their swap function. However, the capability offered at mingovia.org/else/coins is different. What you can do there is upload your wantlist or extraslist as a spreadsheet, formatted in a standard way. This gives you access to all the tools and power of using a spreadsheet, including sorting and filtering.
Numista is still great! Here, there is already a huge database of users, and each user has a history of swaps. This gives us a basis for trust.
My website will hopefully expand the opportunity to find coins to fill holes in your collection.