I got a Hero5 session last week, and I'm loving it so far. Seeing as they're practically the same aside from resolution I'll give you my experience so far.
How I use it:
I use mine on my helmet, to replace my previous setup (Hero 4 Silver w/ Sena Bluetooth Backpack). The Hero 4 is now mounted on the bars facing towards me, and the Session on the right side of my lid for a POV shot. Audio comes from my Sena 20s linked to the GoPro backpack on the bar mounted Hero 4. Result is a much lighter helmet, less drag, and I can now turn my head without the camera catching my shoulder. Syncing audio and video from 2 cameras takes a little extra work, but easier than expected and for the result its worth the extra effort.
Pros:
- Lightweight (74g, Hero 4 weighs 147g with housing)
- Low profile mounting options, less drag
- Simple one touch operation, turns off automatically when you stop recording to save battery
- 1080p60 in a far smaller camera
- Waterproof to 10m without a bulky housing
- Supports 3.5mm external mic (Hero5 Session only, with seperate adaptor)
- I find the construction feels more solid and well built (Than my Hero4 Silver), less plasticky
Cons:
- Menu system can be a pain to work with such a small screen and 2 buttons, compared to touchscreen on my Hero 4 Silver.
- Lack of touchscreen also makes setting up for angles more tricky, requires using wifi for fine tuning
- Built in battery. No more swapping out batteries, get yourself a portable power pack!
- Battery life. Built in 1000mAh battery lasts just under 2 hours in 1080p60 with wifi turned off. Bring a portable battery pack
- Not waterproof if you use a mic or charge on the go, the waterproof door must be removed
- Hero4 Session not compatible with external mic
- USB-C port. If you had a micro USB mic or other accessories, they won't work without the seperate adaptor (Again, Hero5 Session only)
As a B-cam, or with a full size camera to support as in my setup, these cameras are excellent. However I wouldn't like to use one as my main camera or on its own, unless purely for insurance purposes with no audio.
Only things that made me pick the 5 over the 4 was the 4k capability for future use, and external mic support, just in case. Though the 4 is still more than capable with 1080p60 which is what I use daily for recording rides. With the loop recording function of the Hero5 Session, it'd also make a nice little dashcam for the car, keep it plugged into the cigarette lighter for power and you're set.
Also consider the bitrate of the 4 Session and 5 Session. The 4 maxes out at 25Mbps, whereas the 5 is capable of 60Mbps, hence 4k capability. Higher bitrate = Higher video quality. 25Mbps of the 4 is still good for YouTube and as a secondary/backup camera. As a reference, I export my videos in HD 1080p60, H.264 @ 30Mbps. Higher bitrate also means longer export times, larger files and longer upload times.
Heres a simple guide to show the correlation between resolution and bitrate:
LD 240p @ H.264 baseline profile 350 kbps (3 MB/minute)
LD 360p @ H.264 main profile 700 kbps (6 MB/minute)
SD 480p @ H.264 main profile 1200 kbps (10 MB/minute)
HD 720p @ H.264 high profile 2500 kbps (20 MB/minute)
HD 1080p @ H.264 high profile 5000 kbps (35 MB/minute)
So do I like it? Yes! I've added a second angle to my videos without adding excess bulk, the quality is great, and aside from the menus it's simple to use.
Is it a primary/main camera? No. Not for motovlogging at least. Mainly due to battery life and the risk of getting caught in rain with the waterproof door open to use a mic.
Hope this helps
Also helps me out as I've just written the script to my next video