I only have the H107L, but it is a great little quad. I've been very rough on mine. The first floor of my office building has been gutted for an upcoming renovation so it is very similar to a parking garage. Concrete floors, concrete ceilings, concrete columns, exposed pipes. I've had many hard crashes into concrete columns and iron pipes with resulting hard landings upside down onto concrete floors from a height of about 10ft. Subsequently, I've had to replace just about everything! My son flies his mostly around the house so his crashes are mostly onto carpet or grass. Subsequently, he's only had to replace props.
Learn how to solder, if you don't know already. It doesn't take mad skills and I'm still learning soldering myself. But if you have to replace anything, you'll need to solder. Buy extra parts, especially propellers. The crash kit is a good start.
I bought the larger 380mAh batteries, but don't like them as much as the 240mAh batteries that came with it. The increased flying time is not really that significant and they fit way too snug and change the balance of the craft. I don't hate them, but when I buy more batteries, it will be the standard 240mAh ones. But I think the D uses the 380mAh batteries by default, so this may not apply to you (unless you're thinking about getting 500mAh batteries).
I ordered the prop guard at the same time I ordered the X4. It shipped from a company in China and, a month later, is still not here. Pay a couple bucks more and order it from someone in the US. I wish I could tell you if the prop guard was helpful or not, but since I still don't have it I can't say.
Hopefully I'm going to get to play with a coworker's H107D later today. If I have anything specific to say about that model, I'll do so.
