Yes, the D5200 has about the same sensor performance as the D3400, but the 5200 is not compatible with the NEWEST AF-P series lenses. the NEW AF-P 70-300 with VR is a fantastic performer on the D3400, according to Thom Hogan's review of that camera and lens; he states that the D3400 and 70-300 AF-P VR lens focuses like an expensive 70-200 lens...the D5200 is older, and does not support this NEW AF-P lens protocol. But it does have the flippy screen. The issue is going with an older, not-current model, and not being able to buy and use the AF-P VR lenses. The ability to get a FAST- and SURE-focusing 70-300 AF-P VR lens is a major plus for the D3400 buyer; again...NEW camera models have the very latest technology (AF-P compatibility), but the 5200 has the flippy screen, while the 3xxx series cameras do not.
To me, the
biggest feature is AF-P lens support in the D3400, and built-in Bluetooth so you can send a 2MB photo to your smartphone for sharing or for e-mailing, etc..
As far as battery goes....a 1,200 shot CIPA battery comes from test-firing, with every-other frame being a built-in flash shot, and this is Japanese industry's own testing, so it's honest. A 1,200-shot Nikon battery means an entire week of shooting without a recharge for many people, or two big weekend days of shooting, without a charger and charge-time. A 380-shot battery means...charging much more often. CIPA battery life figures are not entirely about the "one day" issue, but also are somewhat indicative as to how long the battery stays up and is charged, and how long the camera is actually ready to be used for.
CHECK OUT the live-view focus speed, and the HUGE advantage the AF-P 70-300 lens brings to a D3400 user.
Nikon D3400 Camera Review | DSLRBodies | Thom Hogan
Faster Live View focus than any Nikon before it. The 18-55 AF-P VR he calls better than any produced before. He states that to get a better camera, spend another $100 for the D5500: QUOTE "consider
the D5500, which is US$100 more. For that extra money you get a slightly less rough-at-the-edges camera with a fully positionable touchscreen LCD, a flash with more power, 14-bit raw, exposure bracketing, and a better autofocus system that extends over more of the frame. "