Trying to buy a robotic cleaner is a difficult task. Very little info and lots of cash involved make hitting "add to cart" a tough commitment.
I had a Dolphin Diagnostic that was about 3 years old and I gave it to my Dad last year when I got my Dynamic from Costco. My Dad's ran about 10 feet before it quit this year. Not good. My Dynamic wouldn't climb the walls anymore and the suction seemed poor despite a clean filter. Luckily I bought it from Costco so it's going back. I was a huge Dolphin fan until I used the Blue Diamond. When working both do the job but an analogy would be comparing a K-car to a Lexus. YEah they both get you from point a to point b but which would you rather drive? Even that isn't accurate though. in order to be accurate the Lexus only cost 30% more than the K-car.
Based on my previous service history (excellent) with Watertechcorp I decided to buy the Blue Diamond from pooldr.com. I think the website is difficult to navigate and a little cheesy but they delivered promptly so I can live with it. They have an OK return policy of 2 weeks and free shipping. Still, at $1300 it isn't cheap. The blue pearl is about $400 less with a cart. The difference being cleaning time of 3hrs vs. 1 hr and the warranty of the Pearl is 1 year as opposed to 4 years. Apparently the Blue Diamond also uses better internals.
The Blue Diamond is a very similar concept to the Dolphin although it is much lighter and maybe a little wider. The cart rolls easier but I don't think it looks as good as the Dolphin cart. I also don't like the fact that the power supply is under the unit where water can drip on it but it is waterproof so I guess it doesn't matter. It aso has a clever handle that allows for easy untangling of the power cord. Quite handy.
The unit started right up and the first thing I noticed is that it is much more powerful than the Dolphin. It created quite a wake on the top of the water surface. It also has a very random pattern. Where the Dolphin (when set to floor only) would stop and turn, the Blue Diamond turns while moving making arcs in the pool. This is a much better method and it was able to cover my entire pool without any problems. It also clombed the walls with ease but didn't spend much time at the water line while I watched it (only about 5 minutes). That's OK though, I clean my waterline manually anyway. It could have done the whole waterline though I just didn't see it. It must have a sensor in it that tells it when it begins to climb a wall because as it goes to vertical it reverses in the other direction.
The filter bag is much less cumbersome and easier to clean than the Dolphin.
I have only used it a few times but so far it's just a much better unit that functions far better. I can say it cleans better but wether or not it will last longer without any repair issues only time will tell. A 4 year warranty is really good though.
Faster - 1hr vs 6-8 hrs
random cleaning pattern
more thorough cleaning
better wall climbing
easier to clean filter bag
Cart could be designed better but it is functional
reliability unknown - although can't be worse than the Dolphins...
I hope this helps someone else make their decision. Any questions feel free to ask.