IF you go for the ETTL-capable flash unit, you keep open your options and have scope at some future date to further expand your capabilities. If you choose manual-only, you will still have the capability to light your indoor portraits. What you would lose would be the ability for future expansion.
Really, it's a matter of:
- Buy MANUAL. Fulfil current requirements, spend less, close the door to future expansion without another purchase.
- Buy ETTL-capable. Still fulfil current requirements, spend more, keep the door open for future development if the need arises.
Personal choice would be to go ETTL unless you are positive
that you will never, ever want to do anything other than basic 'throw-some-light-at-it' indoor portraiture. It would be the cheaper option long-term. You can always use an ETTL flash (well, most of them) in Manual mode so nothing lost other than the higher initial expenditure.
It's your money, only you know your future needs. Got to be your choice!