I have seen guides with statements that evacuated tubes are up to 70% more efficint than flat panel systems.
Its funny that you never see any reference to the fact that evacuated tubes can break relatively easy compared to flat panels (which are much the same strength as a cars windscreen), in fact some companies will supply additional glass tubes when you purchase a system from them.
Many companies supplying evacuated tubes import them (mostly from ...you guessed it....CHINA).
If you install any type of solar heating product on an existing hot water system YOU WILL NOT BE ELIGIBLE FOR STATE OR FEDERAL GOVERNMENT REBATES.
When you look at the cost of tubes/ panels then add installation you will find that it is cheaper to install a completely new system.
Buyers should also find out where and who will service any products you purchase...there are a lot of "sales" people selling products and that is all.
My suggestion is use a reputable and local supplier who will sell, install and service the system you buy. Make sure you talk to 2-3 suppliers and find out what the boost capacity (when using electric boost) is.
Make sure that any solar hot water system you buy has an REC value, this basically means it has been assessed by the powers that be.
Get quotes from companies who will call to your home, at least you get to meet the sales person and they get to tell you where it is best to install your new system.
Dont rush into your decision, you only get 1 chance at rebates,