A sensible project manager always tries to hand pick his Trials Installation aircraft. Saves a fortune on time and cost. But the squadrons hate it.
On my last programme, after being stripped to nothing for over 2 years at Westland the TI got a visit from the sqn AEO. He walked up to her, patted the nose and said "That's my baby". He'd told me, fuel and oil and she'll fly forever. He was right. 5 months saved on programme. Refund from Westland, paid for a couple of nice-to-haves. Everybody happy.
The Proof Installation was a dog. Hardly serviceable during main trials. TI did the work of both.