I had a 4 stroke 50cc Chinese Supermoto, I liked it but would I recommend one..... probably not. It was reliable for the most part, but in the first 50 miles went wrong quite a few times, mostly electrical woes involving the ignition. I bodged something from one of my dads old jap bikes and some waterproofing spray and it ran great after that in all weathers. But, bits started to fall off such as gear lever, rear rack, an indicator... All bolts were made of cheese, suspension was poor, it was heavy and had about 3 horsepower. The finish was appauling, I cleaned it often with WD 40 on most metal surfaces and washed it and it rusted before your eyes. The whole exhaust went, air filter housing, the engine started to corrode and discolour... It only broke down once though after those 50 miles (throttle cable snapped) and was my first bike so I loved it! Looked okay, stupidly bulky for the engine it had but it served its purpose. My parents kindly bought it for me brand new for £1100 and I sold it for £750 and gave that back to them. I did about 8500 miles I think.
The chain was worn, the nylon rear tyre was worn, the stanchions were rusting, the rear shock bearings were creaking, the front brake disc was warped and corroded.... But it ran like a trooper, especially compared to my mates 2 stroke Chinese 50cc which was absolutely pathetically slow and blew rust coloured gunk out the exhaust all the time. He de-restricted it and replaced the exhaust which had about 1/2 a litre of water in it and it blew up 2 days later. Was quite nippy for those 2 days though.
TL:DR - I would avoid personally, but if you have to look at the pulse adrenaline they seem to be alright for some people. I would just get a Jap built 125 though as they are far more reliable and easier to work on. Honda CG 125, Yamaha SR 125 or YBR 125, Suzuki GS 125 theres some examples. Korean bikes are slightly better than Chinese, Hyosung seem to be half decent. All of the above can be picked up second hand for the same as or less than a brand new Chinese 125. Never buy a 2nd hand Chinese bike....