Manufacturer's instructions are usually reliable, and should be followed. If it is an Estes kit and something goes wrong (if the adhesive doesn't hold together and the rocket crashes) they are pretty good about replacing your rocket. The only time I would suggest ignoring the instructions would be if you came across an old kit that still called for the use of Testors model cement glue-in-a-tube (that stuff is worthless, even for plastic model kits).
If you have not ever worked with epoxy before, there are some basics you should know. It is a great adhesive when it is used properly, but it is also a pain in the rear when it is not.
First of all, it uses a chemical reaction to harden (it does not 'dry' like white or yellow water-based glues) so if the instructions say to mix one part (by volume, usually) of this tube with one part of that tube, they mean ONE part and ONE part. If you get this ratio wrong you can easily end up with a mess of goo that never quite hardens, never completes the joint you are trying to build, and leaves a huge mess to clean up (with lots of rags and alcohol).
Because epoxy hardens (and does not evaporate part of the material like water-based glues), you will pretty much get a relatively heavy joint. Whatever amount of epoxy you put into the project will remain there---this stuff is generally pretty difficult to sand off with sandpaper or to file away with other tools. Epoxy tends to make heavy joints unless you develop an eye for putting in only what you really need.
Different epoxies come labeled as '5-minute' or even '30-minute' and that pretty much means exactly what it says. You can count on the fact that your 30-second quick-set epoxy will be unusable at (or very quickly after) 30 seconds after you start mixing them, so do not mix the whole package and expect to have the whole afternoon to be able to dip some out of the pot and keep on using it. Further, within that labeled 'pot life,' you can expect your epoxy to be truly workable (or, usable on a practical level) for about half or two thirds of the pot life. It will start to thicken up and turns more viscous, and cannot be worked into tight spaces as easily.
I like to mix epoxy in small batches and work on one assembly step at a time, rather than lay out a whole bunch of ready-to-build joints and try to hurry through as many as possible before a batch of epoxy starts to go bad. And I keep the left-over epoxy from each batch for a while (over to the side of my work area) to inspect it later; I want to know if it hardened properly and if I can expect the rest of it (inside the joints) did the same.
If it gets on your clothes, or onto things where you don't want it, or (more importantly) onto things where your teacher or Mom doesn't want it, you are in trouble. It doesn't come off easily (like, at all) when you want it to. It is extremely easy to mess up clothes, table tops, etc.
Many people develop allergies to the epoxy (some start off that way before they ever use it once). Others try to use latex gloves to keep the epoxy off their skin and end up with allergies to latex.
Epoxy will soak into balsa, cardboard and paper parts and will make a good structural joint but you have to catch it when the epoxy is fresh and fluid and can soak into those materials. Epoxy will bond very well to plastic parts but the joining surfaces MUST be clean (no obvious dirt, no finger oils, clean off the mold-release coatings from the injection molding process with an alcohol wipe-down) and it helps to give the smooth plastic surfaces a light scuff sanding with fine-grit sandpaper to give a little more mechanical grip to the adhesive.
Cured, finished epoxy is a plastic, and will often soften when exposed to heat or to strong sunlight. It also gets brittle with age, but we are talking MANY years here usually. If your build project is around a long time the joints that were bullet-proof when young can become amazingly fragile when they are old.
Unless you are joining materials that just simply won't work with other adhesives, epoxy is generally not necessary. (It might work well anyway, even if it is not absolutely required.) If you can use something more simple or cheaper or easier to work with, I vote for an alternate adhesive choice every time.
