There is nothing wrong with the approach that you have taken, but what if I want to remove the 3rd row of 5 then I cannot. For this reason most people will add the delete button to the repeating row (so that each row has a delete button). Then I can eliminate the row that I want instead of just the last one. If you decide to do this then you can change the command to be:
....removeInstance(this.parent.index)
This.parent.index will return the subform number that the button is on and hence it will remove the correct instance.
Just thought you might want to consider a different approach.
You can see this in action in the samples that ship with Designer ....look at your install directory at the subfolder structure below for a good sample.
EN\Samples\Forms\Purchase Order\Dynamic Interactive\Forms
Paul
