Very interested in an app of this kind, but wouldn't buy it without trialing on my data. Too many content-specific gotcha's could render it ineffective, amazing

Very interested in an app of this kind, but wouldn't buy it without trialing on my data. Too many content-specific gotcha's could render it ineffective, amazing or anywhere in-between. A time-based trial could be good in that respect, and as a benefit for the developer gets a satisfied user hooked-in and not wanting to lose access.