Yeah, differences are:
- limit on extra txns is 100 txns at any one time (by default), which is a fair bit smaller than 20MB
- all evicted txns go through the extra txns pool, not just those at the top of the mempool (so it doesn’t prioritise top of mempool txs)
- the extra txns pool isn’t indexed, so what’s evicted isn’t prioritised
(All of which only matter if there’s enough replacements going on that top of mempool stuff isn’t already being kept around long enough)