The partners appear to work both sides of the deal, which is great for them, but can spread them thin and make them entirely inaccessible to you. The benefits are expensive, but there is some play on the pre-tax savings side, so if you think you are paying too much for insurance, note a given plan, for example, also has a quarterly kick into your HSA. Be sure to shop around for insurance, healthcare.gov can be almost half as expensive.
If you are being abused by the account, Vaco's hands are tied since the client is revenue stream and your are (merely) the talent.
Don't expect regular reviews or raises, so when you go in , you have to go high and be sure to work Vaco for whatever raise you think you deserve. These sort of activities can be a bit embarrassing and uncomfortable for tech talent. Be sure you can make the case with specific data for raises/more PTO because "everyone else gets it" doesn't cut it. (And never should)