I'd take an RDB over any of the Canadian-manufactured AR180-derivatives with the possible exception of the SAI R18 Mk2. The design is arguably KelTec's greatest, with the rifle's operating system simplicity in itself. Everything hangs off of the barrel, making field-stripping a fairly simple and straightforwards process. I found the RDB that I owned for a time to be surprisingly accurate and (once the gas was balanced) superbly reliable. The RBD has a factory trigger that is better than most rifles, let alone all other bull-pup designs that I have tried. There is minimal after-market support for the RDB, but then again if nothing breaks or requires upgrading then there isn't much to be done. The biggest single upgrade that any owner can and should make to their RDB is to buy and install the KelTec-branded Aluminum MLOK Handguard, which retains the quick-detach feature of the original, plastic Handguard. The aluminum Handguard considerably "stiffens" the entire rifle, improving the overall feel and balance of the firearm in addition to providing ample MLOK slots for the addition of a Vertical ForeGrip, Flashlight and/or Laser(s). The alumiminum Handguard should be considered a mandatory upgrade. Beyond the Handguard, MCarbo makes aluminum Triggers, reduced-pressure Trigger Springs, and so forth, so minor upgrades are available for those who wish to tinker further.
As others have noted, the only things that led me to sell my RDB were the fact that it has no military pedigree (and therefore does not "fit" my collection), and the requirement to pretty much field-strip the rifle in order to clear the rare (but still possible) stoppage. The latter in particular, is a deal-killer for any "serious" use. That said, as a recreational sporting/utility rifle the RDB cannot be beat for $1500 New retail. IMHO it is a far superior design to the Canadian-manufactured AR180B derivative rifles such as the WK-180, WS-MCR, and so forth. YMMV.