My experience (albeit over a year ago now) was that the main problem with claiming is that your claim doesn't get processed until a new tenant is in the property. So there could be a gap of a couple of months between when you receive rent from your last tenants and when you retenant, plus then add a month or two for your claim to be processed.
CGU Landlords insurance are very competitive when you own multiple properties (we are through REI Brokers so can't speak of CGU directly as to price). I have had occasion to claim twice and have found them excellent to deal with. Can't see any reason for having to wait for new tenant in the property - actually they even pay quickly on the initial rent loss and then again at the end of maintenance and repairs for the remaining amount owed. Can't speak highly enough of them.
Just be aware that REI (who I go through- underwritten by CGU) will give you a discount only (about $30 cheaper than the last one) if all your properties are written on the same insurance certificate and sent to the same address. I just found this out today, as I had to redirect the insurance from the managing agent to my own address.