Seems pretty good, so far I will keep using it.
Nostur does use the “since” filter on relay feeds, and it won’t add older posts above newer posts when updating the feed, not sure if that breaks anything
Discussion
It doesn't break it, the relay disregards since/until filters, but it does provide a specific order that's not timestamp based (score based) - so it should work much better if you trust the order the relay gives you