I’ve used a teak Sadolin interior wood stain. Teak is quite dark and seems to work ok. Although I find it takes a bit of playing around thinning it. Trying to get the right balance for what you want it to do.
I’ve used Quickshade and it is good and you do know where the extra money has gone. But a dark wood stain picked up from a discount store can be cheap as chips. Plus Quickshade has a short shelf life; Water based Wood stain doesn’t so much.