If like me, you are beginning flying RC helicopters, there are two things you must buy after the heli itself:
Firstly, you need some gel superglue. About half of those plastic cams, links and stuff on the main rotor and tail plane will have broken within a month of you starting practicing. You can of course buy replacement parts, but as each little piece of plastic generally retails for three quid, it gets pretty expensive quickly. Gel superglue works wonders putting it all together. NB - the normal superglue (the stuff that comes out of the tube like water) is useless for heli parts.
Just put a dab of gel superglue both on the crack/break and also around it. Then, if the part has enough clearance, wrap some sewing thread around the break. The gel glue will stick this thread around the break, giving you a lightweight 'RC helicopter part plaster cast'. Even without the thread, gel superglue on its own is usually enough (as long as you have the patience to leave it to cure overnight!).
Secondly, you need a training kit like this one. You need a training kit no matter how much you have practiced on one of the micro co-axial indoor helis (they are much easier to fly, and doesn't prepare you for a single rotor heli) or a PC based RC simulator (real helicopters have all sorts of weird responses - especially just before a crash!).
For example, most rc helicopters take off diagonally to the left rather than straight up (because of the action of the tail rotor on take-off). It takes some practice to allow for this, and without the training kit, what will actually happen is that you will panic, overcompensate, and veer into the ground (well, that's what happened to me!). Using the training kit in this situation prevents the heli rolling over onto its side.
Physically, the training kit is a simple `X' shape that prevents your heli blades ploughing into the ground on takeoff and landing, as this is the most common cause of breakage for the useless beginner (a.k.a me).
The training kit fits on your skids, and acts as a 4 way stabiliser for when you land/take off. It also slows the heli down, which is useful for the beginner. I use this training kit quite comfortably with a Honybee v2 (one of the most common outdoor training helicopters). and can fit it snugly without using any ties: I just jam it over the top of the skids, and the tension keeps it there. Once you have a training kit fitted, and assuming you always make sure the rotor power control (left joystick if you use the most common 'Mode 2' configuration)is pushed down to zero at the point of crash, you will usually get away with zero damage for all but the most serious crashes.
A few of notes on the trainer itself:
It's light and pretty durable... well, more durable than the heli it protects, but that still doesn't mean anything in the rc heli world other than 'it won't break often'.
A previous review mentions that the central plastic strut cracks. Yes it will, unless you push the metal rods all the way in, which is actually a tight fit. If you do that properly, it lasts forever (by `forever' I mean `I've so far spent £80 on a helicopter, broke £40 pounds worth of parts on it, and this training kit is one of the few things that I haven't broken yet). And if you do break it, well, thats where the gel glue comes in.
You don't get instructions on how to build or attach the training kit, but there's loads of help and advice on youtube. Especially important is the fact that you have to balance your heli after attaching the training kit. Basically, your helicopter is properly balanced if it hangs straight when lifted by two fingers placed under either end of the flybar.