The Vac-U-Lock system keeps the attachment more in place and does not allow it to slip around, but the o-ring design allows more contact and stimulation to the wearer. Harnesses without Vac-U-Lock are more attractive generally and better in design, but the Vac-U-Lock system certainly is better in staying in place.

You could always buy the Vac-U-Lock Dildo and put it into your o-ring harness. less

Disclaimer: I don't have any Vac-U-Lock products, so the Vac-U-Lock comparisons are based on what I've heard from others and pictures.

Provided that you have a properly sized O-ring, and O-ring harness is quite secure as far as the harness-dildo link. Some dildos have stronger bases than others, so they stand up better, but during use a properly sized O-ring will not let your dildo come loose during use.

From what I've seen, the Vac-U-Lock harnesses don't seem to be as well constructed as the midrange to high-end O-ring harnesses, and they don't look like they're nearly as adjustable. The Vac-U-Lock dildos that I've looked at haven't been silicone, either, so they're harder to take care of and more prone to problems. I thought at one point that I saw an adapter that would allow Vac-U-Lock dildos to work in an O-ring harness, perhaps it's this link. If your Vac-U-Lock dildo has balls it might work in an O-ring harness even without an adapter.

In general I'd say stick with your O-ring harnesses and look for a compatible dildo. You'll probably be happier in the long run. less