All results obtained by automated scanning can be erroneous ;)
Rules only get to release status when we're confident they are as robust as possible, so you can hopefully be more confident about those, and similarly beta plugins may well be more robust then alpha ones.
Note that all new add-ons / plugins must start at alpha and then go to beta before they can become release quality, so they could actually be very robust just not have had enough exposure for us to promote them.
However all plugins should run within a reasonable length of time, and clearly the Advanced SQL Injection plugin isnt doing that in your case.
Could you raise an issue for this?
I'd recommend turning it off for your application - it should definitely not take that long.
Cheers,
Simon