Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
I think there is a huge difference between 15-20 newtons but not so much between 35-40. But I agree with getting the mesh up to the recommended level set by the manufacturer. I went from static alums to shurloc ez's and newman rollers so I went from 15 newtons to 30-60 right away and I noticed a huge difference in quality and most importantly, setup times. I take our 205N mesh up to 55-60 initially but I settle it in around 45 once I've used it a few times. I keep most of our newmans in the 30-40 range, depending on mesh count. I've gotten 156's up to 60 newtons, 110's up to 55 newtons but I don't keep them that high, it's too much work for only a little return.
The shurloc ez's won't settle at that high of tension, they'll be in the mid to low 30's once work hardened. That is still a good level to be at when you are used to printing with low tension statics. I think the shurlocs are worth it, but I prefer the newmans when it's all said and done. I'd sell all our shurloc ez's if I could replace them with newman rollers, but they are a huge part of our business and they do a great job. They are very low maintenance compared to newmans but I still think the newmans are worth it in the long run.