It is better with a diffuser. But is it absolutely a mistake to not get one? Only if the counter is dark and shiny. Those are mirrors.

I don't have tape lights (considered them but chose differently), but I did see tape lights without a diffuser at someone's house -- I did not like the effect, it was like straight line of small bright circles running along the countertop. She has a dark countertop, maybe that makes the difference, IDK I never saw anyone else with them IRL. Just get the diffuser, they're not that expensive.

The only time I’ve used a tape light without a diffuser was at my mothers house which has corian (no reflections)

Some of the newer LED light strips don't give you the pin-point lights. No diffuser needed.

@chispa, can you link to those?