Try Hondata, they make many different ones for the OBDII GSRs and they even come in different stages to suit your needs. You can check them out at Hondata . I believe these are some of the best ECU's out for Hondas and from what I've heard so far, they are great. Hope this helps.
This here on TI was posted on Sept. 10, 2002 and could have been found using the search function if one enters the term "Mugen ECU" in the search box to the left of this page. It answers your question and gives you the links to the Hondata analysis of how useless the Mugen ECU is and my article HERE which explains why you should do a reprogrammed ECU last and why it should be a custom one and NOT a Mugen.
the purpose of one-size-fits-all, best guess pre-programmed ECU's?: it's quick like an intake. plug and play. no brainer for people who don't understand tuning and don't want to. But then because you are living in ignorance, you don't get the gains or as broad a powerband compared to a properly done chip on a dyno on your own car.
No. when you clear the codes, it erases them entirely. It's a PROM. I believe there is an article on how to reset the ECU for beginners by Surfer X in the Maintenance section of the Articles. I guess you've been here a long time but maybe never checked out the articles yet. You may want to take a peek at them since they may contain useful info like how to reset the ECU and other things.