Can't really give much in the way of tips or advice for a strut tower brace other than just get the one that you like best. They help... slightly, but nowhere near as much as a set of sway bars.
Brands to stay away from? Probably not. I've had a $45 ebay one, JZS147 Aristo one, and now a RMM one and I didn't notice the slightest bit of difference switching from one to the other. As for used prices, that'll totally depend on the manufacturer and condition.
A strut bar is designed to reduce this strut tower flex by tying two parallel strut towers together. This transmits the load of each strut tower during cornering which ties the two towers together and reduces chassis flex. To accomplish this effectively (especially on MacPherson strut suspensions), the bar must be rigid throughout its length.
To answer your question they do work. you will notice better improvement on corning and overall feel of the front end.. Its not only used for Aesthetics. There is benefit...
My reason for the question is if the chassis is designed well enough, then you won't notice a diff in hard cornering with/without the bar. But if people really notice a diff, then there is weakness in the chassis. Just wondering what people have noticed by installing them. The one I found is $75 used, but looks pretty beefy.
My 91 Bonneville I added the SSE strut tower brace and then I added the 87-89 Deville front end to strut tower braces both, and the car was significantly more solid in the front end.
The cross brace is technically a a Monte Carlo Bar. If you can add the brace from the firewall to the strut towers, those are Export Braces. These are old terms from the 60's that were born out of the racing programs. Largely with the help of Carrol Shelby.
From past readings our chassis are designed pretty weak from what i recall... Hence the vibrations at 60mph?
I really wish more companies would adapted to the 3 point strut bar in more vehicles like in the mustang like you mentioned. Much stronger and rigid than the 2 point bar. By just adding the strut bar you should "feel" a difference and only gets better when you add lower and rear sway bars. I added a strut bar in my Optima and noticed a difference right away in cornering and highway speeds..
REALLY helped a lot. All factory braces, the front end to strut tower was from a 87-90 Deville and the Monte Carlo bar was from a 1991 SSE Bonneville/1991-1993 Deville/FWD Fleetwood (About $67 new at GM), I still have the Monte Carlo bar for the 91 SSE/91-93 Deville. Fits a LOT of GM cars from 87-99 (C and H Body cars) It it too low to fit the GS, but it isn't far off.