I had a GP-E2 on a 5D3 - I never liked it. Sure it works, but separate battery you need to keep charged daily, with a separate charger you need to take on the trip, needing another outlet at the hotel,[..]
I solved that specific issue with a USB AA charger, it was €4 or so at the local Ikea. I can charge pretty much everything off a big powerbank or laptop overnight nowadays: watch, phone, camera, AA batteries.
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The software to use the GP-E2 (on a mac at least) sucks (like all canon software), the file format it creates for tracks is a proprietary format needing conversion.[..]
The recent update gives you 2 options: NMEA 0183 and kmz. NMEA 0183 isn't proprietary, but the Canon implementation does report a fix, when it actually hasn't. GPSbabel has a gpgga=0 option to fix that. But you are correct that it needs converting, almost no photo tools accept NMEA, it's pretty much a GPX world out there.
The current UI is a lot less awful than it was in the Map Utility days, I only need to use it when I go out shooting with more than one camera. I really don't understand why Canon makes it so awkward to use, why can't it automatically import all logs when connecting?
Same goes for automatically setting the clock to match the computer, there's a setting in EOS utility do exactly that, but for some reason it never actually does. Same for the Canon Connect app on the phone, it keeps disabling the "Automatically sync time with phone" toggle. And you can only set time over wifi, not bluetooth. And no option to set the time from a timeserver on the internet either.
The "set time automatically from GP-E2" option does work, thankfully.
That time sync issue is what really bugs me, since the internal clocks on my RP and M6II go out of sync about 6 seconds each and every day, which makes syncing up the geotags a pain.
All in all, I personally find using the GP-E2 in the hot shoe less work than using a separate logger, but Canon could make about every step in the process a lot less painful just by changing the software a bit. And use higher quality RTCs in the cameras.
There, rant over