Bearing in mind I normally ride a BMW RS100 Iwould suggest that the little 125 gys are a good buy providing you set them up well and dont expect a modern bike performance.
Areas to watch are poor use of bolts and washers with no locknuts or nylocks.
Carburation issues which need adjustment of the needle either bottom or next to bottom needle notch also the richening of the tick over mix (visible at front of carb under neath).
Headstock adjustement after a few miles to take up slack.
Greasing of spindles and pumping grease nipple on swinging arm, the nipple is on the n/s and is very small either change it to EU type or an adaptor.
Fit LED bulbs as the rear ones are a pain to change. Same for pilot bulbs and speedo See LED bulbs ebay
Check all the wiring and secure plugs together through the use of a cable clip pulling the ends together.Loop through cables
Bind and clip the wiring and remove the big plastic sleave in the headlamp which will allow the cables to locate easily, sort out and reroute to smarten up.
Change the sprocket to 44 tooth and possibly 17 front this will give ROAD gearing. standard sprockets 15 0ver 56 which is fine for off road.
Boil the chain in chain lub as required and check sprocket bolts as these act as drive pins to the hub.
The speedo was in kph and officially a no no so use acycle speedo which will run as kph or mph you will find that it runs about 10% fast ie you arent as fast as you thought.
Great little bike ideal for shorter journeys or where a big bike is a pain.
Change the oil frequently and dont loose the filter or spring wash out in solvent and watch for metal bits as with any engine.
Plastic damage simply repair by roughening the rear side only wipe with cellulose thinners, cut small overlapping patches of cotton or glass fibre cloth work in rapid araldite and flex the damage to take in to the cracks dont wipe the area to remove surplus When near solid ligtly scrape any spills.