I would defiantly get the firmware updated. Garmin Pilot does this for you automatically. If you do not use it (Pilot), there are offers for a free trial period, which should allow you to do it. If your has super old firmware, then you may need to have it connect via the serial port to one of the Garmin handhelds, which will do the update via the hardwire. I did get one that had original firmware that turned out the only way I could update was via the Area 660 and the hardwire. Later versions didn't have that issue. I couldn't complain the eBay seller thought it was broken, so it was beyond dirt cheap. If you do not have access to a hard wire setup and yours will not update via bluetooth, PM me and I'll give you a hand.
The GDL-39 is a very handy unit. While it is a bit "Captain Nemo" looking, its form factor allows remote mounting in rather limited space. The A version, with AHARS is also a super little unit. I have used it to ferry aircraft with non-functional HSI's back from halfway around the world. Not to even start any kind of "best oil" type discussion. I personally settled on Garmin Pilot a few years back because it actually works internationally. Foreflight's world kind of ended at the border. This is not an issue of 99.99% of the folks on this forum, pretty much just me. The other nice thing is it plays well in a hard wired installation, which I prefer.
As you can see the GDL-52 up there in the Caravan's turtleneck (and a Spot), which is actually hardwired to the Area 660 on a flexible old cellphone stalk. I simply used the standard Garmin 12V hardwire between any GDL and the 660 or the 796. They have ones for virtually any model they made. I recently got the -52 version for the Nexrad capability, which works everywhere. The Caravan's built in Datalink system just went offline as they discontinued the ground station service. We where on our way out to Rosevelt Lake for a day of practice. The little Husky showed up perfectly as we where doing our work on the lake. As did the FIS weather letting me know it was going to be a slow groundspeed day back.

We where there to do some of this kind of work
