Pretty good actually, not a well used one for sure but i found they worked a treat, check which model you go for as older ones dont have taps on pipes or a primer
But other than that, they seem to have a WAY better lifespan of a Fluval filter (eg it lasts longer than a month or two before needing spare parts!), better media capacity too!
Possibly not the turnover of an eheim but tbh i just hate ehiem filters, its a personal thing, i think the cost far more than they are worth.