To me, this also seems somewhat non-transparent and imprecise.
Perhaps we could consider implementing the possibility for the user to choose whether he will always insist on the fastest fee or wait a few blocks for a normal or low fee. It is very important for small transactions.
Your idea is good, but it would be complicated in some cases based on network congestion. Because when choosing lower fees, sometimes you might need to wait longer than expected, even it would take a couple of days to be confirmed on the blockchain. Have you remembered when the BestChange campaign had been running? Their payment takes a long time to receive in our wallet. I can recall, due to lower fees, sometimes after a day we received it.
Remember we encountered such a situation a year ago; the transaction fees were high. Lower transaction fees take a couple of days to confirm the transaction. So if b1exch adds a lower fees option, then sometimes we may see such situations, and users may come here or on the scam accusation board with the allegations.
So even with the lower fees option, it needs to be monitored and updated from time to time. Otherwise, we may see complicity.