Question about Garmin Hrm-Tri

That will probably not be entirely satisfactory. I think you will get hr, but not while swimming. I recommend a new Fenix. That was the best update away from the 910.

Since both products support the ANT+ standard, this must work. But I would buy the HRM-PRO right away. It can also support BLE. Then you are also open for other connections such as Zwift or other watch brands etc.