Our good friend Kev knows Festools, so it is wise to seriously consider his advice.
Perhaps my advice is different, because I have been earning a significant income working with wood for over 60 years. My current shop is very large, with 6 other master cabinet makers and often several helpers.
Before Granat was distributed by Festool in the USA I used Rubin in the coarser grits and Brilliant II in the finer grits. Once Granat became available in all grits and in quantity, and I became convinced of its benefits, in early 2011 I started using Granat virtually all the time. It does cost more when you buy Granat, but it lasts so much longer it saves money that way. The long life of Granat also save labor changing sheets.
This is important to my bottom line, but for a DIY person, it might not be the best thinking. Because my shop does not perform finishing functions, generally our clients specify that we stop at 120 grit. I stock Granat in all sizes much finer than that and also coarser than 100 grit although we seldom use any Granat as coarse as 80 grit or as fine as 180 grit. But, most DIY woodworkers make a far wider range of projects then I build.
Your ETS150/5 is a marvelous first sander, and there is a lot to be said for sticking with 150 dia paper as long as possible. While you are gaining experience, Rubin, Rubin 2 and Brilliant II are very good choices for smoothing rougher wood, removing old finish and so on. Having a wide choice of grits and styles of abrasive I suggest is far more important in DIY than calculating the savings of using one particular type of abrasive. Just because I only use Granat 99+% of the time hardly means this will be true for anyone else.
Personally I see less than no point in traveling to a dealer which does not stock the Festools I need and all the accessories and supplies to support those tools. Since Festools have been distributed in the USA there have been highly qualified and experienced on-line dealers who not only can ship the tool you need, but also all the vital accessories. What use is a sander without a selection of abrasives? The leading on-line Festool dealers sell abrasive kits, even in Systainer if you want. I probably have as much Festool abrasives in my supply room as most of the larger dealers, but I still bought kits in the various sizes. Of course I re-fill those kits as we use abrasives and keep track of how many sheets of which kind are needed for the re-filling. This is how I stay in business, because I can allocate the number of sheets used on a given project.
Oh yes, over the past few days a member or two have complained that some of us write pots that go beyond a couple of lines. Well, some topics need a full explanation. I also think it rude to post without proof-reading, but then that could just be me. Your mileage might vary.
