I consider myself reasonably qualified to comment on this, owning both the Orion Shorty Plus (same as Celestron Ultima), a 2.5X TV Powermate, a scope with very sharp optics and a boxfull of premium eyepieces to jam down the throat of both barlows. I have also been doing this looking up thing for a long time and used a truckload of different barlows over the years, from babys not much bigger than a plossl eyepiece, to a 2" 1.75X Parks barlow that has the physical dimensions of a can of tennis balls and weighs about the same as a brick. Heavy enough in fact to unbalance the 16" dob I was using at the time. I will say that we have never been so fortunate with barlows as we are today. They are infinitely superior to what was available even 15 years ago and if you buy something of reasonable reputable quality today, you get a very good product.
In answer to a couple of questions that are foremost in your mind
1) Did the guy at York Optical sling some at you when he said the Celestron Ultima is about the best barlow on the market ? Absolutely !!! He is either slinging some at you, or has never used the best himself. There are 4 that come quickly to mind that are superior to the Celestron Ultima that I have used. The Televue 2.5X Powermate, the Televue 2X Standard barlow, the Takahashi Extender Q 1.6X which are all more expensive than the Celestron Ultima and the the Orion Ultrascopic 2X which is a little cheaper but only by a couple of $$$.
2) Is there much difference between them? No
3) Is the TV 2.5 X Powermate better than the Celestron Ultima? Yes
4) Is the Celestron Ultima a very good barlow? Yes.
5) Is the 2.5X TV Powermate worth the extra money over the 2X Celestron Ultima ? In my case the answer is yes. It is a little better, but not by much and many people couldn't justify the extra cost.
6) Why is the powermate better ? Thats a hard question to put your finger on the answer specifically, its just a tiny bit nicer IMO. I think it has slightly better contrast and performance off axis and also it preserves exactly the eye-relief of the original eyepiece. It is as close to "not using a barlow" as you can get. It just disappears.
7) Did I get a good barlow and good value for money? Absolutely. You have a great barlow and haven't wasted your money.
Some advice for future reference ? Ask next time before you drop the coin. You didn't get burned in this case but you could have.
CS and enjoy it.