I often list invoices overdue and want to review the invoice history of a customer before I send them reminders or call them direct.
Clicking the customer name in the invoice list takes you to the Customer | Profile tab it would be better to recognise the original context and go to the Customer | Transaction tab.
Also, currently the default list of Transaction is 'This Year', come Jan 2019 by default no transactions will be listed and the fiddly way to change the default date is to select the changed from date AND click run. It would improve the work flow to list by default the last 12 months of transactions (or at least have that as an option) AND initiate the run action on a change of date and remove the Run button. This would reduce the mouse interactions required by half. The drop down options include Last Year, but this list Last years transactions and no the most recent, a 'Last 12 Months' would accomplish this.
Also the Date Picker does not select a new date when the month or year drop down is changed, it should default to either pick the same month day as was previously picked or if no longer a valid month day, it should default to the first of the picked month.
Whilst I am at it, it would be nice to retain at least a summary of the customer name and contact details on this page too somewhere so we know who we are talking or need to talk to.
Lots of good ideas here, although as well as last 12 months as an option you could also have next 12 months and allow your preferedoption to be made default. Thumbs up to making the transactions page the default page when selecting a customer and also the date picker (this also happens in other date pickers in Kashflow and can be extremely frustrating)