The proposers themselves will not read your review. The DFG office will treat it as confidentially as it expects you to treat the proposal which you have in hand. Where appropriate, it will pass on your comments without, however, revealing your identity. In its individual grants programme, the DFG can award substantially less than half the funds applied for. Your assessment is sought with the aim to identify the best applications for funding.
Every research project is different from all others.
Therefore, what you write down will rest on your own judgement. Constructive suggestions for saving money are explicitly invited.