There's a huge difference between: Hi, your service as it is would not be adequate to my use case, here's why if you want to know and possibly change it. and:

There's a huge difference between: Hi, your service as it is would not be adequate to my use case, here's why if you want to know and possibly change it. and: Can't believe you do X instead of Y, what a waste of time, this doesn't help me at all.