Just wanted to post a few insights into Viiiiva in the hopes of being helpful, and providing some answers to questions that I was unable to find before ordering.
This summer I've found myself using Strava a lot, and really liking it. I enjoy the social aspect particularly, and since I do power training on a Cycleops 300 Pro at a studio all year round, I've also found that actual on-road rides have taken a secondary role in training, and are really used to evaluate progress in the studio. I also figured the HR derived power estimate that Powercal kicks out has to be more accurate than the weight/speed only estimate I was getting from Strava. With that as the backdrop, let me explain what I was hoping to do with Viiiiva.
My goal with Viiiiva was to get my heart rate, power, speed and cadence data into Strava on my iPhone while maintaining those data inputs to my Garmin 500. HR and PWR come from a Cycleops Powercal, and SPD/CAD from a Garmin sensor. I was hoping to continuing wearing Powercal, and just have the Viiiiva in my seat pack, converting the Powercal and Garmin ANT+ signals into Bluetooth LTE for my phone to pick up.
My phone is the iPhone 5, and I have both Strava and 4iiii apps running on it.
Okay, so my first effort was to connect everything through the Viiiiva and run it into the 4iiii app. iP5 connected to Viiiiva through their app no problem, but the 4iiii (okay, all these 'i's are getting really annoying; hereafter, Viva and 4i) app only recognized the Powercal as a power meter. I was hoping the Viva could only act as a conduit, and that HR could be selected to be sourced from another unit (Powercal), but that's not possible, apparently. When Viva is hooked up to the 4i app, Viva is the HR by default, and is not changeable.
Next, I went to the Strava app, which according to 4i web documentation only had some partial compatibility with power coming out of a Viva connection. DCRainmaker talked, in his Viva review, something about layered channels of data and rotating transmissions for devices not 'smart' enough to look for and understand the layered channels, so I thought this was the scenario 4i was talking about.
Still wearing the Powercal, I was unable to get a consistent connection to Strava via Viva. It seemed my BT icon on the iP5 would flicker in and out. Once, I got it connected to both HR and PWR, but it dropped out. I restarted the phone, tried running 4i app simultaneously (with and without Viva connected) to see if the BT problem was related to something there, but it seemed to have a mind of its own.
Without getting into all of the permutations of wearing dual HRs and apps closed or open, let me just say that Viiiiva is not the answer for those looking to link a Powercal. I just couldn't make it transmit both HR and PWR simultaneously to either 4i app or Strava app. Which kinda sucks.
I'm not prepared to have my iPhone strapped to the handlebars, and so I want to keep my Garmin Edge 500 out there, while the phone records from my seat bag. I guess I could ditch the phone and just upload to Strava after the ride via Garmin Connect, but it's so much easier just going straight from the iPhone.
Wahoo has a new version of RFLKT in the works that should be able to work with both BT LTE and ANT+, so maybe that'll work for me by replacing the Garmin.
If anyone has any ideas about how to solve this problem of getting biometric data onto both Garmin and iPhone at the same time, I'd love to hear it. I think the answer is a discrete power meter, like the Garmin Vector or the ubiquitous Powertap hubs, but I'm also curious to see what RFLKT offers.