I think any compatible (ANT+ etc) HR strap will do it...
I got an LTHR measurement with my Tickr X before i upgraded to the HRM-RUN. I like the HRM-Run better for the way the strap connects. The Tickr's snap mechanism would commonly come unsnapped.
Lactate threshold requires HR data that includes HRV data. My understanding is that some non-garmin straps do not transmit HRV.
Maybe. HRV is part of the ANT+ standard. If you broadcast in ANT+ you have to send RR data. Most chest straps can detect HRV. Optical HRMs have a bit harder time doing so at higher heart rates. The Wahoo issue was that they transmitted some HRV oddness when connected via ANT+. It works fine in BLE for whatever reason. The strap you are buying *might* be just fine, but you won't know till you try it. The best way i've found to view the HRV data is via Runalyze. Set the watch to log HRV data and have a look at the HRV info once the fit file syncs to runalyze.
If it doesn't work, return it to amazon and buy a different monitor.