I think most customers would prefer to know that this is going to cost me $99/month till I hit a certain level of XYZ and that you will contact them when they approach that level to move up to the next plan.
Plus for your benefit I think you'll make more money off the tiered plan (depending on the service you are offering).
While everyone wants highly engaged customers who are getting maximum value out of your service I think you could have months where a user just doesn't log in to view their data that often, it's still there, still providing value but they might only login and review once per month.
Are you going to charge them $99/view?
On the flip side you might have users who login 4 times per day so they are both getting value but costs would be very low vs. very high.
I think tiered plans work better.
Take this feedback with a grain of salt as it may depend on your service/offering.
But for most SaaS I'd rather see as tiered as both a user and the owner of the SaaS app.
