I hear a difference in tone with the un-slotted bridge-pin modification as it sounds mellower and fuller than the factory original slotted bridge-pin setup. As the commentator mentions he can hear and feel the guitar do better things with the un-slotted modification. I just keep my guitars as they came from the maker which is usually with the slotted bridge-pin setup. Slotting the bridge-pin holes will bring the ball end of the string closer to the line of the bridge saddle as projected through the guitar's top. If a player wants to mount a Soundboard Transducer (SBT) system to the bridge plate and directly under the saddle line, the ball ends of the strings could interfere with the proper mounting and thus the functioning of the transducers.

SBT examples: Trance Amulet, K&K Pure Mini, James May Engineering UltraTonic 3.2, LR Baggs HiFi, Dazzo.