I fly indoors from time to time, but the Spark is a bit big and generates a lot of airflow for indoors. I've found it's "attracted" to walls due to the downdraft of air it generates, so flying down narrow hallways can be a little intense sometimes. If you see it drifting toward a wall, over-correcting can send you flying into the other wall. I'd also give a nod to prop guards, they're pretty much required indoors although I have yet to bump anything. Grass probably won't damage your props, branches are iffy, but a
bookshelf is pretty much guaranteed to cost you a prop or two. It'll also clear the papers off your desk if you get very close!
A special consideration with the Spark is the collision avoidance. I have problems in my house doing things like going through doorways because it sees it as an obstacle and will stop at the threshold. I either have to back out of a room or switch to Sport mode to disable the sensor. Of course that triples the sensitivity of the stick so you have to be careful. Lately I've
only flown in sport mode indoors so I don't have to fight it, and I think that gives me good practice with being "gentle" on the sticks. It seems to do a good job of parking when you let go of the sticks though, guessing it's using its optical sensors to hold position even without a good GPS lock. (my house is mainly GPS-proof)
My hexacopter (WLtoys Q282-G) is by far the most stable indoor drone I own, I actually never even bother with the prop guard indoors. It doesn't fly very fast and is a lot smaller with less downdraft so it can hover near a wall and has plenty of maneuvering room even in a hallway - they're great for a beginner indoors. My Syma X11 are a lot more maneuverable, and stick sensitivity is a lot higher so I usually fly those with the guards on, although I rarely have issues. The syma (with the guard on) are beaters, I wouldn't be too afraid to run into a tree with them and pick it up and toss back into the air and get going again, so they are my preferred indoors drone because they're rugged and more fun to fly. So if you would like something for indoor time I would really suggest you get a cheap beater like the X11, they're much better suited for indoor use than the Spark, and you hav a lot less risk all around. For about the cost of a
Spark battery you can go to amazon and get an X11 ($29) with 5 additional
batteries and a bulk charger ($15) and basically fly as much as you want indoors.
