I had TJM on my first 4wd long before I'd heard of the name ARB, it's not like TJM are Jonny Come Latelies by any means.that was pretty much my understanding of the current situation also.
As far as I know TJM were started before ARB, but I could be wrong on that. Either way, they've been going for a while.
I have always found ARB overpriced. I believe in supporting companies that do their own R&D on their own products rather than just copying others but the price still has to be justifiable. In some cases I've also found their design philosophy to be a bit "just like the last one" which doesn't always work.
I was going to buy a Ranger and was looking at canopies. ARB's Ascent canopy was somewhat pricey BUT I felt had points of difference over others (such as the hidden side window locks etc) and therefore was justifiable and I probably would have got one if I'd bought the Ranger.
On the other hand for the bar work on my 200 (which I bought instead of the Ranger) ARB were a good bit more expensive than TJM for a bar that seemed to be an inferior product in my opinion and didn't suit the car as much as others. In that case I though their prices were overinflated and not justifiable. When you see some of the ARB showrooms you can see where the money goes though!
For me the 3 criteria I look at when buying stuff are:
1) Did they design it, or copy it/design it to a price? - I prefer to buy from companies who designed it, even if it cost more. If you buy a copy you're assuming that the company who were too lazy to design it themselves were competent enough to copy it properly. If it's designed to a price then you'll get what you pay for.
2) How vital a component is it? - If it is something that you're going to expect to save your life or you are going to depend on it greatly then perhaps the extra money for the better brand is worth it for peace of mind, both on terms of quality and overall support. If it's just a "nice to have" then risking the lesser brands stuff could well be a good trade off to save money.
3) How often will I use it? - If it's something you will use very often then again, buying the better brand is probably worth the extra money. if it's something that you'll use once every blue moon then the lesser brand may be worth the punt (pending the answer to point 2).
That's just my take on it. Everything has a value proposition and that proposition is different for everyone depending on the expectations of the product.