Parts-by-the-hour - issues
The conventional wisdom is that these OEM supplied contracts achieve most for their clients when they fly more than 400 or so hours per year, but that 'wisdom' hides a truck-load of questions which might lead to a YES or No answer for you.
The significant issue concerns the perception of PBH/SBH contracts and what it is thought they deliver and what they really do deliver. This can only be determined by carefully reading the contracts and seeing whether the contract guarantees parts availability (with compensation etc) or simply parts 'when ever possible'... or 'when available'. The two approached are significant when you are clutching the contract in-hand and drumming your fingers on a desk waiting for a part you thought would arrive v quickly and for which you now wait with a grumpy owner asking why he signed some contract.
If the owner signs the contract, what does he expect.....? A guarantee that his helicopter will be 's' whenever he needs it.....? If that really is his motivation, get the contract read very carefully before recommending it or signing it...
Warranties on helicopters are, at their best, pretty awful bundles of documents. The airframe is covered by one, the avionics by another, the engines another and so on. The admin of all of this when flying loads of hours can be a task in its own right.
The 'gotcha' clause tends to be - if you have a snag on your helicopter, you have to diagnose the problem (at your own expense), and with a telephone line open at the OEM factory, remove the part and (all at your expense) ship the part to a factory gate - which might not be where you collected the bright new machine from. Then, at the OEM's discretion, you sit and wait (with a part absent from your helicopter) while the OEM considers what it will do. Only then will a decision emerge and a part may come back to you finally shipped at the OEM's expense. You may still get a bill for pro-rata use of the part you sent back.... and the new part's own warranty might still only last until the anniversary of the original new aircraft warranty!
The answer to your question is found, as the phrase, goes buried in the details of not one contract but the several you will need to cover the EC135's total system - engines, airframe, avionics, and customisation. The same applies to warranties where the cover may vary from avionics to engines.
I wish I could say YES... go for it at 150 hours per year or NO... don't... but there are simply too many factors involved and I've only mentioned two.
A gut feeling suggests that you might simply get the owner to pay the full PBH/SBH rate for engines, airframe, avionics etc. into his own helicopter account as hours accrue to fund the necessary spare parts and associated costs, but make sure the owner understands that there are no guarantees that the part will be with you when you need it.
PS.... PBH and SBH contracts tend to have lists of the parts they cover... unless you feel rich and go tip-to-tail.