Some quick facts: West system epoxy is basically an unfilled epoxy made as a laminating epoxy I am not knocking it but just want you and others that may read this to know some of the differences of the epoxies being talked about on this thread. West system would be good for laminating fiberglass cloth to a plywood fin or fiberglass cloth to a cardboard tube or something similar. That is why West system epoxies have a thin viscosity of less than 1,000 centipoise, so the epoxy can flow around and into the fiberglass cloth, that is why they are called laminating epoxies. If you are purchasing a kit that has a filament would tube with G10 fins this would not be near as good a choice as using a filled high strength epoxy because you are not laminating the fiberglass cloth or fiberglass thread into a tube, the filament wound tube and G10 sheet manufacturer has already done this for you, you are at this point needing a high strength structural filled epoxy to assembly the tube and G10 fin and components for the best results. To use an unfilled epoxy similar to West System you would first need to add lots of fillers and thickening agents to make it anything even close for bonding strength to a filled high strength structural epoxy such as Rocketpoxy G5000. Rocketpoxy G5000 is in an epoxy classification called filled high strength structural epoxies. That is why Rocketpoxy has a viscosity of 350,000+ centipoise (basically a paste). If you love to formulate epoxies and have the time and knowledge to purchase, add, and mix the correct amounts and types of fillers needed to make a superior high strength filled epoxy then the west system unfilled epoxy is for you, if you want a high strength structural filled epoxy to use right out of the jar where an expert chemist with lots of test data has already done all the hard work for you by adding and mixing in the exact formulation of fillers then use something like the Rocketpoxy G5000. That is why filled epoxies do have better physical properties than unfilled epoxies for structural assemblies such as filament and carbon fiber wound tubes, G10 and carbon fiber sheet products, metals, plastics and generally any composites. Most serious composite assemblers that wish to use an epoxy ready to build with will prefer them, also that is why filled epoxies may cost a little more than an unfilled epoxy.
Also when comparing Rocketpoxy to an epoxy such as the Bob Smiths 20 or 30 minute epoxy or Proline 4500 the Bob Smith and Proline would be more brittle and have less bonding strength with some composite materials especially plastics and aluminum. Yes one of the major tradeoffs of a higher temp and faster setting epoxy is that they generally become more brittle. We feel that Rocketpoxy G5000 is the perfect tradeoffs of high strength, not brittle, curing time, and a decent temperature rating that is good for about 98% of all high powered flights. You may have a little more of a learning curve with the Rocketpoxy and may have to be a little patient about the curing times but it will give you a great finished product where lots of fin flexing and even some hard landings will not crack the epoxy. Ill give you a quick test you can do put about ¼ - 3/8 inch layer of your West system, Proline , and Rocketpoxy G5000 epoxy into a plastic cup and let it harden, then whack all your samples with a hammer, you will notice quickly which epoxy did not shatter like brittle glass ( hint the RP G5000 will not easily shatter) , you will also notice which epoxy bonding strength stuck to the plastic cup and which epoxies ere easily popped off (you will not be able to separate the Rocketpoxy G5000 from the cup). You can have a higher temp and faster setting epoxy but if it is very brittle and less bonding strength this may cause failure well before any temperature comes into play. Im not trying to get all the West systems, Bob smith and Proline users pantys in a bunch, all these epoxies have their place and I sure as well know how this forum can get at times and not looking into getting into a big back and forth with this. If it works great for you more power to you, Im just trying to answer a few questions I have been asked about this. Since my company is the Manufacturer of Rocketpoxy I do feel it is important to get the facts straight from the manufacturer who has actually done a lot of lab work and test data on this.