Donic Formula rubber
 

Heard a lot about Donic Formula (F1, F2, F3, F5). Can anyone give me your experience/opinion about them? Is it really like rubber speed-glued?

I'm not playing them myself but one important thing I heard about them is that they aren't very long-life - someone in my club had to change only after about half a year - and now he's come back to Sriver doing speed-glueing on this one...