Aloha Aaron,
The strategy does work. It's been around for years, under a lot of different names/companies. There are two primary strategies. First, you have your mortgage with a HELOC on the side to help pay down the mortgage.
Second, you replace your entire mortgage with a HELOC (the plan you described). One of the caveats with this plan is the variable rate. Either the HELOC needs to be paid off in the three years ($33k per year) or you'll have to refinance it into another HELOC. Another caveat is discipline (or lack of). Once the HELOC is in place, your minimum monthly payment drops, increasing your disposable funds. Those funds need to go towards paying down the balance as quickly as possible, not used as play money Also, as the HELOC gets paid down, the equity is still accessible, meaning you could withdraw funds for things like a vacation, car, etc.
You do not need to pay for these services. It is a pretty simple concept. The one benefit of these service providers is they provide some level of accountability for you. Someone to report your progress to, which may help with the discipline dilemma.
As for using the $170k for investing, that is a little trickier and will need a sound investment plan. The funds could be used on a short term basis, but in the long run (when the initial interest rate adjusts) the monthly payments will likely result in a significant swing in cash flow (negatively).