As already mentioned and I only can stress it again - Even if you are on the road at slow speed you can still "unhappily put on the face" in an unexpected situation.
Some really cheap unicycles are offered which are not "brand goods". I made this mistake once when I spent €110,- on ebay for a used noname-wheel. It was equipped with a grotto-bad algorithm that made driving very uncomfortable. Every time you have reached the top speed of approx. 16Km/h and used the "Tiltback function", which should slow down soft, there was a "powerless dead center" while you were slightly tilted forward on the wheel. This has led me to constantly feel like falling off forwards and braking as well-but backwards. Now it lives decomposed in the basement because only the tyre suitable for spareparts.
If I talk from "no noname", above I have to list here at least some well-known brand manufacturers: Ninebot (Segway), Kingsong, InMotion, Gotway, Rockwheel, Airwheel and IPs.
Hands off from anything with less power than 800W (unless it is for a child). The engine power is not simply needed for speed, but to bring you safely through potholes and overboard stones or abrupt ground waves. If your weight is more than 50 to 60Kg, there has to be enough power to ensure a successful reerection if you are stuck in a pothole for a fraction of a second at full speed and lose the center of gravity.
In general unicycles with 67V and 84V technology are offered. 84V models are usually a little more expensive but better. The higher the voltage (V), the less ampere (A) has to flow over the power lines and over the motherboard to the motor. 67V models generate more heat especially in heavy loads and run more risk to burn the power mosfets or even solder joints and cable insulation can melt. 84v models, on the other hand, are less susceptible to this because they produce a little less heat . But they can get quite warm, too.
The battery is the most expensive part of the unicycle and the more Watt hours (WH) the more expensive it is. You should not completely drive it empty if possible, but you should not always charge it to the max. To maximize the lifespan, you can get a "charge doctor" that only charges about 80% of the battery. By the way: rechargeable batteries get tired in the cold season. If you are able to run a distance of 30km during the summertime so it can be significantly less (down to more than 50%) at temperatures around the freezing point. You might think the battery is broken, but next summer everything will be back to normal.
- Hands off from No Noname wheels