Well no, like the link I posted... You just open steam://store/1607720 in your browser and it will ask you to open it in steam. I'm assuming this should also work just the same with the overlay api, or in fact even better because it's using the steam browser protocol.
SteamOverlayAPI.OpenURL("steam://store/1607720");
You can try right now. Just paste the link into the adress bar and hit enter.