There are a few things to keep in mind when you’re using aftermarket detail sets…
The first is to check to see which model kit the particular set you’re interested in was built for. Sure, you can adapt a detail set to a different kit (if I can do it, so can you), and it will probably save you time over scratch-building the details. But you’ll probably (probably, not definitely) get a better fit if you’re working the kit that the person who did the masters worked from.
Second… Keep in mind that the person that did the masters the molds were taken from most likely did NOT use CAD/CAM to build the master(s) (though I’m sure it’s just a matter of time before 3D printers start being employed). There’s a talented person somewhere who scratch-built the masters using the kit (that I’m hoping you’re using) for dimensions and shape. Talent, as you’ve probably suspected by now, is a massive variable; some have more than others do. As a result, the degree of accurate fit to the resin parts is also going to be variable. Some sets are really works of art, others your 12 year old nephew could do better. Unfortunately until you have the set on hand, you can’t tell how good it’s going to be. Certain aftermarket suppliers have better (and deserved) reputations than others and as you go along you’ll develop your own internal database as to whose parts are worth the cost of acquisition and whose are not.
Third… CHECK YOUR REFERENCES. Check them frequently. Sometimes people get things wrong (yeah, ain’t that news…) and that includes the person who did the masters. In my limited experience, there’s a WIDE range of accuracy problems.
If you expect to buy an aftermarket set that will just drop into your model, you’re going to be very disappointed. There will be a lot of fitting and adapting to do. And don’t expect that the aftermarket set will include all the details you want. Aftermarket sets will save you tons of time scratch-building but my experience has been that they’re not complete and require me to add things…and sometimes remove things…from them to get what I’m after.
Resin parts are unaffected by styrene cement for reasons I hope are obvious…THEY AREN’T STYRENE, they’re resin. Depending on how “fine” the join is, you’ll need either epoxy or cynoacrylate glue – superglue – to do those tiny joins. The problem is that the tip of the superglue tube is NOT small enough and if you try to use it straight from the tube you’ll end up with a massive blob of glue that eradicates details. My method is to make a small puddle of glue on a piece of aluminum foil. Then I will dip something small into that puddle to transfer the glue to the area of the part(s) I want to marry.
There’s a few ways I can do that. If it’s a SMALL part (like freakin’ tiny brackets mounted to the side of a tank’s turret that rucksacks and gear hang off of), I’ll use the tip of a needle or a straight pin to transfer the glue. I have fingers that are much larger than I want them to be sometimes so instead of wrestling with just the pin or needle, I’ve mounted them onto convenient-to-hold things like a wine cork (for the needle) or an old chopstick (for the pin). When I have two parts that have to be touching before being glued, Micro-Mark sells a handy glue applicator (it’s in the middle of the photo):
Okay, that applicator is nice. But once I was looking at it, it reminded me of something and it didn’t take me long to figure out what. It reminded me of the head of a needle that had had the tip of ground off. I checked Micro-Mark’s applicator against a needle and damned if I wasn’t correct. So. If you want a similar applicator (and having one like this is VERY SODDING NICE), make your own applicator. Grind the head of a needle off until you have an open-ended fork and then mount the needle into the handy…well…handle of your choice. And by making your own applicator(s), you can tailor the size of the applicator to the size of the job, only being limited by how small a needle you can get.
So these aftermarket sets will save you a lot of time. They will rarely just drop in and expect to add things that you’re going to want included.