It would be nice if we can only show add-ons for a service if the parent service is in the same currency. At the moment you can see other currencies even though the parent service is in a different currency.

For example: My service is in GBP £1.00

But I can go to Manage > Addons and see Add-ons for:
Add-on 1
One-time: $1.00
One-time: €1.00
One-time: £1.00

And not just the following:
Add-on 1
One-time: £1.00

As it means that the customer will be billed in two currencies, and could mess up accounting.