My 2p worth:
If you can get used to flying the Seneca under instruments in 15h, then brill- go for it. Otherwise I'd opt for a bigger proportion on the aircraft.
It's only so that you can be completely familiar with the nuances of different aircraft when you go for test: the school I was at had 3 Duchesses, one of them basically refused to slow down as quickly as the other two. Another one had one prop about 500rpm different with the same lever position, which obviously takes extra capacity to sync the props. It's little things like this which, in themselves are insignificant- but as soon as you sit Mr. CAAFU Examiner next to you, they have the potential to cost you an extra £2000 unless you know about them, and how to deal with them.