I haven't looked at the dvd tablet system, I figured when my kid is old enough to need it, I'll just use the iPad holder and they can use that to watch videos. It looks like it mounts almost the same way as the dvd tablet, you just provide the iPad.
Your 50i will have the standard suspension with the air suspension in the rear, so it should ride like any current X5 with 20" wheels with the third row, if you can find one to test drive. If your 2010 had the Sport package, you had adaptive drive, which will have ridden quite a bit differently then the standard suspension. The current Sport Activity package doesn't change the suspension at all on the 50i, the M Sport and/or 3rd row both add the rear air suspension, if you want adaptive drive, you have to order it as it's no longer included in any package.
15 BMW 328d xDrive Sports Wagon M Sport
15 Audi SQ5 Prestige
13 Honda Insight EX