I'll start with the good points:
1. It will create a report and allow you to export it by emailing
2. The report format is a .CSV file that you can open in Excel
3. It's the best expense app I've found for the iPhone - but that isn't saying much
Now the weaknesses
There are very few expense fields - all it has is the date, client, project, amount, expense type and a notes field. I need a lot more fields like:
1. Location of expense
2. Report number field
3. Currency (Euros, Yen, etc)
4. Exchange rate
5. Vendor (restaurant, hotel, airline, etc)
6. Client name (person's name for entertainment expense)
7. Client title or function
8. Receipt ID (number or file name)
As it is, the only way to add this extra information is using the Note field; but that's a lousy way to do data entry.
It would also be nice if there was a field for the mileage reimbursement rate. This isn't absolutely necessary because it can be added in Excel when the report is export to my computer, but why not?
This program seems to be well written and easy to use, but really lacks features, especially considering the high price (by iPhone app standards).
I won't be using TDFTracker as currently written. I recommend buying Documents-to-Go and making a simple spreadsheet to record expenses.