I bought Checkbook 1.x over 2 years ago, and use it everyday. It has always been extremely stable, never crashed, and always accurate in its calculations. Lately I was wanting it to have more control in terms of reporting and being able to group together expenses in ways it did not yet offer. I started seriously thinking I may have to switch to another app because 1.x wasn't making my tax time as easy as it should be. I had gotten Money and Cha Ching in some bundles, so I tinkered with those for a day, but they weren't as comfortable to me as Checkbook was. Then I saw 2.0 came out, and with the Pro version too, which was perfect timing for me.
So, I upgraded to Checkbook Pro. It does those things I needed, and then some! I had also wanted to be able to make column changes on many items at once (a la iTunes), and now it does that. I had over 100 entries that I can now alter the Type, Category, etc. in one step. Nice. WIth 1.x, I wanted running balances and an additional column for Category. Now it has that. And, although it's still the same stable software to which I had been accustomed, it has now become exactly what I need and want. In my opinion, it is the best out there.