Keep in mind each baby is different...
I have a 4 month old and started using these part time with a prefold at month 2.  The velcro works great and I agree with another reviewer they are stretchy.  I was able to get a decent fit.  However, no matter how tight a seal I had, I would get some sort of leak.  I also felt that these were not easy to wipe clean like other covers.  After I found I was not satisfied, I tried gDiapers on a whim.  I don't like how those close but the lesson I did learn is that leg gussets are a must for my LO.  They keep the prefold in place and also contains any messes.