Hey Henry - with the craftsmanship of the RD that is only evident when you run one firsthand, I'd imagine they will run a very long time. Its probably the finest piece of equipment in our hobby - period.
I would agree with Chuck totally - Deltec is a great product. I put BK, Deltec and H&S in a category completely by themselves. They are all constructed perfectly, researched and optimized to near perfection.
There is a premium for the BK, but I think the skimming for dollar quality is pretty equal. There is no doubt that the BK300 ($2500) is much stronger than the 702 2x1260 ($1700). But its also $800 more. I'd put the 300 more inline with the 1003 3x1260 ($3100+). There is another great choice of H&S 3x1260 A300 for $2300. I had that skimmer and can say with complete certainty it was as good as the BK300. Its also less expensive, uses Eheims which can be replaced easily. The downside to me is that is louder.
I just sold my BK because it won't fit under my new tank. And I'm using Chuck's old 702. My next skimmer is a VERY tough choice. It will either be a BK250 internal, Deltec 702 or a custom H&S. And it IS a tough choice. I think the BK might be the best, but I prefer externals (can't fit an ext BK under the tank). The Deltec and H&S are a toss up. Deltecs look sexier, but replacement parts are expensive. Deltec charges over $500 for an Eheim as H&S is $299 for the same pump.
As far as customer service - H&S and Deltec have a slight edge here. Getting a hold of someone to help you is probably equal among the three, but getting parts will be MUCH easier for D and H&S. But BK is working hard to change that.
Hard choice, but there is no bad one!