I have used these pumps, but the larger ones in the range. The design is fine--the early ones had a pressure set micro switch which was adjustable, and worked best with a pressure resevoir to stop the pump excessive switching. The later ones used a piezo electric circuit and worked fine without a resevoir of pressured air.
All of the ones that I have used have rubbish bearings. Maybe they are not all like that and I just got the exceptions. The bearings are cheap
to replace with high-quality stainless steel
fully sealed waterproof Japanese bearings of the same size.
My pumps, once the bearings (which lasted a couple of years) had been replaced have now gone on to last about eight years and still counting. I would far rather have paid that twenty bucks or so as an addition to the purchase price
, and not had to remove the pump and replace the lousy bearing.
So--check your bearing. The motors give little trouble as long as you mount them correctly. They like to be mounted as designed. The more solid the mounting surface--the quieter they are. With the new quality sealed bearing they run sweetly and quietly. It is cheaper to replace the bearing than buy another pump.