@Roy Skaggs BoH is very familiar with this strategy. I know of a few people that use this strategy with BoH and I initially got the idea from another investor on Oahu. It's a win win for them to offer these kinds of deals because a lot of mortgages are held by main land banks. Switching over to a HELOC keeps money on the island and saves the consumer a lot of money. Just my 2 cents.
There is a lot of competition between the major banks in Hawaii. I'm not looking forward to doing it over again in a couple years but I get the impression that the healthy competition among the banks works in our favor. BoH doesn't want either of us to go to another bank, much less a mainland bank. I suspect as long as interest rates stay they way they've been we'll be able to continue to enjoy low rates on this kind of financing.
You mentioned credit/loan value. That can be a concern if your numbers aren't right. But so long as you have enough equity in your home, an income that can support a HELOC, and decent credit it shouldn't be much of a problem. It's all in the numbers. @Royce Talbo mentioned using a smaller more traditional HELOC to pay down mortgages. That's something that we did using a personal line of credit (PELOC). We used that to pay down enough of our mortgage to have enough equity to qualify for a 85% LTV HELOC. We did it the same way as we handle our current HELOC. We payed a big chunk out of the mortgage and paid off our car with our PELOC, deposited all our income into the PELOC using it as a checking account, and then we had enough equity in the home to qualify for a large HELOC. And depositing all our income in the PELOC paid it off in less than 4 months.