Is 3M cheaper than other regular rim cement? or better?
No to both. At times Fast Tack has caused problems with peeling carbon fiber off rim tire beds. It creates a bond but won't reaffix if the bond pulls loose, which tubulars tend to do. If you are just riding straight line rides and not racing hard, you may not pull your tire loose, but in that case you could use practically any adhesive. If the idea is to be certain your tire won't roll in a hard turn or on a steep descent, 3M has caused problems for enough riders who do test the limits of their glue jobs. It also doesn't mix well with regular rim cements, so you have to clean off your rim completely before applying Fast Tack, and then if you for any reason need to apply Mastik One, you have to clean off all the Fast Tack. Fast Tack is incompatible with most of the tapes made for cyclocross and is incompatible with some of the newer tape-based products out there.
Over the past 7-8 years a number of us went from happy users of Fast Tack to having serious problems. After a lot of work and a lot of pushing 3M to disclose their changes in the formulation, we realized it wasn't going to work any more. At the time, Vittoria was having some stability problems and was reformulating their own glues for the same reason -- to avoid volatile organics gassing off while it was being applied. Some of us thought we were basically screwed -- no good rim cements left. But Vittoria got their act together and have a product that works really well and is much stabler than it used to be. And all the tire and rim manufacturers have pretty much planned their resins and base tape adhesives with Mastik One in mind -- they warranty problems if Mastik One was used, and they typically won't if Fast Tack is used.