I have never used Opti-4 myself, however I have a brother inlaw that uses it and swears by it. I use Mobil One 10w30 in my small 4 cycle engines becuase it is a proven product and I can get it most anywhere. So far the Mobil has worked great and costs less.

is this the same mobil 1 that you use in automobiles?

Opti-4 is actually not a synthetic but is still excellent oil. I recently sold a Toro mower that carries a five year warranty. The customer purchased a six pack of Opti-4 which doubles his warranty on the internal engine parts courtesy of Interlube.Both it and the synthetics are good choices for air cooled engines if you don't mind the extra cost. They are still a lot cheaper than a new mower. Whatever rows your boat.

I bought a new Homelite mower in 1990 with a B&S 3.5 HP engine. It was the main mower on my small lot until 1994 when I moved to a larger lot. After that I used a Lawn-Boy because it was a mulching mower but still used the Homelite for bagging. Eventually the Homelite was not used at all so I gave it to my brother-in-law who used it pretty hard. I recently cleaned it up for them and did a tune up/blade/oil change, etc. The mower is still in use and burns or leaks no oil and the engine has had no oil-related repairs (just a carb kit and a spark plug). The point is, I used Opti-4 SAE 30 in that mower. I now use it in my Lawn-Boy 10684 (Tecumseh engine). Since most of us only change oil once a year, the extra expense is probably meaningless. Perhaps I would have the same results with a synthetic or some other oil, but I usually stick with what I know works. I also use Opti-2 in my 2-cycles.

Hard to argue with success.

Here it is after the clean-up. The guy had been using old gas in it he had bought for 'Y2K' and I thought it was a goner. I changed out the oil, drained the gas and put an 'E3' plug in it and it fired right up.

Here is a link that might be useful: 1990 Homelite/Jacobsen