I have an original Karoo and my experience has been excellent.
I bought mine “new” 2nd hand from an early adopter and have had it now for almost 2 full seasons of riding. The experience over this past year has been better than my experience in year one. This is because Hammerhead has slowly and steadily improved the software, improving stability and then adding features. The Karoo of 2020 is far and away a more reliable, stable, feature-rich device than the Karoo of 2018/19. Where I used to have frequent sensor drop-outs and mystery freezes, I haven’t had any squirrelly behavior this entire year. It’s been rock solid reliable.
I haven’t plucked down a deposit yet for a K2, not because I don’t covet one, but in rare gesture of fiscal restraint I’m holding off until spring 2021 to make the spend. But, I do plan to get one, primarily because it addresses a few shortcomings of the K1 — it’s lighter, has a beeper, and has a more secure mount. (Mount failures in the K1 were such a problem that Hammerhead offered a free replacement made with stronger materials. I upgraded my mount with a 3D printed synthetic mount and it’s going strong 18 months later.)
I don’t miss the beeper in the K1, but folks with Varia radars or Strava segment junkies really, really, really want one. The beeper in the K2 is a popular move for sure.
Trainer Road outside workouts are not currently supported, but screenshots of TR workouts were part of the original Karoo 2 tease, so presumably, they are on their way. DC Rainmaker seems to think so too.
Battery life has been an issue for some, but not for me. I estimate I could get about 8 hours based on how it’s performed when I’ve gone 5-6 hours and had 40% or so left. When I’m planning more than a six hour ride, I use a USB backup battery the size of a pack of lifesavers that fits perfectly taped to the underside of my stem.
I’ve used Bluetooth and Ant+ sensors with it no problem. Currently, I use the built-in GPS for navigation/tracking, a Bluetooth Suunto Smart HR sensor, and Ant+ SRM power/cadence. All work like a charm.
The screen is brilliant and I love the space and flexibility of field layouts. I have 4 pages setup that I scroll between as I like (a data page, a map/data page, an upcoming-elevation-graph/data page, and a summary data page where I can have things such as TSS, avg & max HR, avg. & max power, temperature, etc…
I don’t have Varia radar, but those who do say the Karoo’s implementation is the best, even better than Garmin’s.
Strava segment implementation is pretty slick too.
And I’ve been very pleased with its navigation and maps. I build routes in RidewithGPS and more recently with Strava after their routes upgrade. Both sync with my Hammerhead account, which in turn syncs with the Karoo. No files to export/import.
Oh, and their support team is awesome. Super responsive and helpful.
Anyway, I could go on.
Consider me a fan of the Hammerhead Karoo.