What I say here counters the instructions you received with a new engine which tells you to use a synthetic oil at 25:1 during break in. They say that from not truly knowing the subject and because they think that gives the engine a better chance of surviving break in. It's a rookie perspective from China.
Proper Break In
The goal is to let the rings wear down some to conform to the cylinder. So using petroleum oil, not too thick, is good and then after break in use semi-synthetic to not smoke much and get good wear protection. These are oils that are "petroleum", without synthetic oil, and recommended ratios of use for break-in without prolonged hi RPM runs; Amalie SynPlus Oil 20W-20 (32:1), Bel-Ray Mineral 2-Stroke Oil (34:1), Yamalube 2R (35:1). You can see that they all hover in the same range of ratios so probably any other non-synthetic oil could be used at 33:1. If you have a ported engine and will be reving higher than the stock 6000 then multiply the ratios by .9 to get the correct ratio.
Good semi-synthetic oils to consider after break-in and their 6000-8000RPM ratios: Motul 510 2T (29:1, 26:1), Bel-Ray SL-2 (32:1, 29:1), Maxima Premium 2 (35:1, 31:1), Motul 710 2T (37:1, 33:1), Maxima Castor 927 (49:1, 43:1), Red Line AllSport (58:1, 51:1), Bel-Ray MC-1 (61:1, 52:1). To read more about the details of these oils and what other oils are available just go to www.dragonfly75.com/moto/oil.html
ps - ratios for break-in are 10% higher than normal (for less oil) and all ratios are based upon my computer program that calculates ratios based on type engine cooling, and max RPM. I prefer semi-synthetic oils because the non-synthetic oils have some properties that the synthetic oils don't have. Of course if you are after the most smokeless oil possible then buy one that is 100% synthetic.
How you break in a China Gas engine is really of not much importance as long as you use the right type oil. That is because proper break in is to help the rings wear down in conformity to the cylinder for better compression. But these chinese engines come with too much ring end gap and so you can never have a really good seal no matter what break in procedure you use. So my general suggestion is just to ride it easy, not too fast, for the first half tank of gas. Continue to use up the gas/oil mix in the tank and then switch to a semi-synthetic oil at the ratio I recommend above.