I used to use sh404sef but found that my users were having session problems and that multi-page threads (in Fireboard) were sometimes broken with the URLs of the 2nd page of threads being totally confused.
I don't know if the session problems were caused by sh404 but the latter was. I was continually trying to mend breakages so I changed to...
Artio JoomSEF, or rather the "fork developed by Kanga Internet
The free version of Artio puts links back to Artio in the re-written pages and it also put's links to "it's affiliates" in the meta descriptions of your pages.
Kanga started out by removing all links and meta-tag inserts but recently he has started putting links back to his domain (but no meta-inserts).
I'm loathe to pay for any of these at the moment because it always takes a while to evaluate how well they are working, or if they are broken.
Mind you I've not thought about approaching the developers (of sh404 for instance) for solutions to the problems I've experienced.
So, for me, the Kanga option of Artio is the lesser of several evils.
I have tried others but can't recall which ones but decided against them over time.