No SD card in the 520.
I have been using a 520 since early January 2016 and a 510 for a year or so before the 520.
The 520 has limited memory available, but much more than the 510 did. I deleted the almost worthless factory map that came on the 520 and installed map tiles from OpenStreetMaps. They work well, but zooming in and out constantly can be a pain.
Overall, I like the 520. It's a step up from the 510, for sure. There are also apps available for the 520. I'm currently using a sort od color screen 'dashboard' that displays my heart rate and current speed using automotive dial type 'gauges'. The gauges are backed up with a digital numeric display and the screen displays other data simultaneously...and those data displays are user customizable and changeable. I have mine set to display total climbing and heart rate as well as distance covered.
So far I've got a lot of rides stored from day 1 and it looks like there is still plenty of memory space still left.
The 520 has been more reliable than my 510, but it did just weird out and shut down 7 or 8 miles into a ride a few weeks ago. After pushing the buttons a bunch of times while still riding with the group, it turned back on all by itself. I lost all the data for that 7-8 miles, but that happened to the 510 a few times and the 510 freaked out repeatedly and so badly it required clearing all data and re-formatting the unit multiple times.
I actually miss the touch screen of my 510 and the seven, count 'em SEVEN, buttons on the 520 can take some getting used to. With winter gloves on the 510 is easier for me to navigate through the screens. People *****ed about the touch screen taking multiple pokes to get it change screens...that was true. And changes were slow, but they did usually work OK in my book.
Garmin units are the devil. But, they are the universally used devil. Everyone has one and everyone *****es about them. Garmin seems to be known for releasing the units with crappy software/firmware and letting us users go through a bunch of fixes and updates.
The Garmin Forums is the best source of information, fixes, work-arounds and opinions on the various Edge units. Book mark it, register on it and use it as required. The tech guys on the forum are really sharp and quick at solving your problems...they have plenty of experience solving the many Garmin issues out there...
My vote is just go buy the damned thing, delete the OEM map and put on OpenStreetMap tiles that fit your riding area and ***** with the rest of us. I think that overall you will enjoy your 520. For the $300 or so for the bundle it's hard find anything that matches the features and the performance (hint: the Polar and Sigma and most other brand forums are equally full of *****ing and complaints).
My only other GPS computer experience was with a three Cateye Stealth 50 units. The computer head, the heart rate strap and the firmware was just a glitchy as Garmin and getting files off the computer head and onto my PC or uploaded to Cateye's Atlas website (equivalent to Garmin Connect's website in function) was a pain more often than not. I liked the Cateye unit...or at least I tried to...before failure upon failure drove me into the Garmin camp.
