I've used this on three engines so far. My purpose was to pre-clean before running ARX. It did its job. Even the dipsticks came clean. Even on a Toyota Slugger.
This is an aggressive solvent type cleaner. Though they don't suggest 20 minute run times I don't think I'd run it over 1000 miles. When I drained the pint fortified Kreen Oil it was clearly solvent impregnated. Be careful on how you use it.
Kano is an excellent company offering exceptional products. Of the Fortune 500 companies 497 use Kano products.
I use Aero-Kroil to clean all of my guns and if you need a bolt to be removed, there is nothing better. This is powerful stuff. JB80, PB Blaster and the like, they can't even compare. At least in my experience. I use their Dry Moly for my guns as well. If you want something to work when it's wet and very cold...use their Moly.
As for Kreen, I think it's a great product. Yet, I recognize it's a solvent based formula. As such, exercise caution in it's application. If you want it clean...use it. Then, embark on a more intense and longer lasting program. Like ARX or RVS. ARX is a great low level cleaner. I'm using it right now in two of my vehicles. RVS has remedial properties. I've read the technical data on both. They work.
To my thinking, start with an aggressive cleaning agent (provided your engine isn't a known slugger) like Kreen. I'd say 500-1000 miles. Then go to a more subtle approach like MMO or ARX. If you don't get the results you need work your way to RVS. MMO is more agressive than ARX yet, I don't believe, as extensive. ARX can help with many other vehicle afflictions like main seal leaks. This is not an MMO trait.
If you need remediation, once you complete your cleaning mve on to RVS. I think I'll have one vehicle that needs it.
It's all a matter of how aggressive you want to get. I'd also suggest as better filtration system once you've done all of this work. Go to the bypass filter section on this site to learn more. Maybe you can find a more certain course for your needs.