OTP Upfront or 7 Day Trial with IAP OTP?

I have been contemplating how to sell my minimalist text based launcher for iOS, Dumbify.

The options are:

• One time Purchase (OTP) Upfront upon App Store download
• Free to download with a 7 day trial period then prompt the user to make a One Time In App Purchase (IAP).

The big pro of making it an upfront purchase is that it is clear to the user that it's a OTP, which is important as there are so many subscription based apps these days.

Curious your thoughts

We are planning to launch in April and have a waitlist