Personally I think it a waste of time as its database is often out of date and frequently throws up results that a site is good when it is malicious and vice versa, though it shouldn't conflict with avast.
The webrep is fixed, the back end server system isn't so hot right now (grey webrep icons when they are down), just don't rely on 'any' reputational tool McAfee site advisor, WOT or webrep, they should be used for guidance only, not slavish abeyance.
It will take time to build the webrep database and bring in the information from the avast virus labs, etc. But it is important for people to keep using it if for no other reason but to build the database up to help it mature.