If its' just the two of you, the Terrano units would work really well. They are full duplex and I'd rate the fidelity as very high. The previous version had good noise cancellation but the new version has excellent noise cancellation. We just finished a biking trip in Florida where we are cycling near the ocean in a 10mph constant crosswind (out and back type of ride) and I don't think I ever heard any wind noise in our conversation at all. Sometimes it was so quiet, I wasn't sure we were connected anymore (we were). The v1.0 units were analog over BT. These are digital over bluetooth. Battery life is rated at 12 hours, and I'd believe that is true but I don't know how that stacks up against your touring hours in the saddle over several days. If you had to go longer on a charge, you can charge them while you're using them and it would be a simple USB battery type interface however you make that happen. The units are small so I'd guess the amount of battery charge required is low probably less than a cell phone. Given that, a very small battery could give you long legs in communication.

The other benefit to the Terrano units is the smaller installation on the helmet in both weight and appendages. It's pretty clean and lightweight. My wife has to be careful and is intolerant of helmet weight due to a neck injury years ago and this works for her. Personally, the long mic for the Sena would bother me. This doesn't have that and the mic does't really extend beyond your mid jaw line. The speakers mount on a velcro strip at the back inside of the helmet and are on flexible gooseneck wires that support them hovering over your ears. You have full situational awareness and you have the advantage in audio quality from it coming from both speakers. I don't have hearing issues at all and I was considering cutting one of the speakers off so it would be just the right side with the integrated speaker and mic assembly.

Finally, you could also have full duplex communication between the two of you and then cellular or Zello style communication seamlessly through the Terrano units. I have tried it with Zello in echo mode and it works fine for outbound comm but I haven't checked how it would work with inbound. This would set up the condition where the two of you could talk in full duplex and then if you wanted to communicate with others in your group, you simply push the Zello PTT button and then communicate over the cellular data network to others in your group.

Only thing you might want to check since you are riding a tandem (if I have that right) is that with any digital system there is going to be a slight lag due to digitization just like in your cell phones. If that isn't a problem, and I wouldn't think it is, this is what I would select since you'll never have a range issue if you're using them predominantly on a tandem.

There is a third option that I'm going to try for our skiing and would also work well on the bike. It's made by Domio Sports called the Domio Pro (https://domiosports.com/pages/domiopro). This uses different technology where it turns your entire helmet into a speaker so no speakers hovering near your ears are required. It uses the cellular data through your phone and their phone app to provided the duplex or simplex communication (you can choose) but it does require cellular connectivity to make it work. The mount on the helmet requires two square inches to attach the speaker driver unit and then there is 1 sq inch required to mount the microphone piece. This could work, but I do worry about cellular connectivity some of the places we ride. It's also supposed to be able (if I recall) to pair up to the BT based systems like Terrano an I believe Sena (not sure if Sena is BT). Their app is similar to Zello but full duplex but I also intend to see if I can make it work with our UHF radios via the BT interface we have for them.

J.