How the compressor will work is dependant on what you are inflating. If it's an air matress or floatie for the river it might be fine. For large truck or RV tires it will be horribly slow. When sizing compressors, PSI is nominal and fairly inconsequental to the CFM output. Manufactureres try and wow the consuming public who doesn't know any better by advertising compressors with very high PSI ratings when they know their CFM output isn't enough to air up a standard tire in anything less than an hour.
Yes if you are airing up a tire that needs 120psi then you need a compressor that will do in excess of that but the higher the CFM the less time it will take to do it. Some of these small compressors might just burn themselves up over the period of time it might take to air up a large RV tire. I would not consider them up to the task at hand for RVs. If all you are doing is topping off a trailer tire then they might be just fine. For myself, I wouldn't waste my money, but that's just in my case.