Well I don't know what phone the reviewer was talking about because I have the new OP6T and the fingerprint sensor is the best I've ever used on a phone or tablet. It's never slow and so far it's been 100% accurate.
I have a number of cut marks on my fingers through a lifetime of work and for example the sensor on my Galaxy S7 was next to useless to the point I reverted to using a PIN. I'm having much the same issue with my new iPad and that too is always requiring me to use the PIN.
The OP6T however is almost an instant unlock and is proving very reliable.
Congratulations on your rare phone, as forums are full of complaints about the fingerprint sensor.