You will need a G2N or a xx8/xx9 series to make use of the Ipilot Link.
Not exactly true:
https://www.minnkotamotors.com/support/compatibility/i-pilot-link
To the original poster: if your Helix 7 G2 is not a network unit (it would be G2N), then LINK will not work.
Also, bluetooth isn’t an additional option. Bluetooth is used with both iPilot and LINK and standard on the new (starting in 2017) motors.
So I think you have a few of questions.
1. Since you don’t have a Humminbird unit that is compatible with using LINK, then do you buy new or used with regular iPilot?
2. To decide new or used, how critical is having good spot-lock?
3. Powerdrive or Terrova?
4. If having the ability to follow a contour so LINK is something critical to you, then you’d need to get a new Humminbird, so even more cha-ching.
If I were you and if you can swing it, I’d recommend a brand new motor with iPilot.