I own an HTS 3500 MK II and love it. The difference with this unit from the 2500 is +$100.00, a volt meter and 3 stage filtration over 2 stage filtration with the 2500 mk II, if you live in an area with dirty power,it may be worth it. I opted to spend the extra Ben for these features due to being in a dirty power area. You may also want to look at Panamax, they do get a lot of good press on this info board.