I installed the double mosmatic z booms < foam brush and high pressure, in 2008 and they are very nice, I have never replaced a seal in them, where as with the single zierden booms that were there for years, I can’t count the times I replaced the cartridge on them before they came out with the conversion kit < the ones that were easier to change with the double O-rings which were allot better < and take more maintenance then the mosmatics ever would, I think the mosmatics are far better than Zierden, cost allot more but well worth the investment.