The original version had a lot of bugs and conflicts, however the new version now available does seem to work a lot better.
Having said that I am posting this on the wifes (my old) computer , without Onspeed, and I honestly can't say the speeds for PPRuNe aren't that different.
Also the Onspeed server tends to store your last viewed pages on its server so when you come back to a site you get an 'instant' display which you are supposed to be impressed with, but you then realise that you have to refresh the page thus nullifying the saving in time that you gained by using Onspeed.
I have coughed up my 25 quid for the year but I doubt that I will renew. I have also had a lot of software clashes in other areas since installing it. (But can't say for sure that it's due to Onspeed)
On the whole it's OK but the hassle of having it onboard at present outways the advantages.
BB