DIY underground downspout UPDATED w/ link

So I would like to have my gutter draining underground. Right now I have one that drains on the walkway to my front door and one that drains at the edge of my landscaping. Currently I have low profile extenders that are mostly covered by mulch in my landscaping. But every big rain leaves a mess of mulch that washes into the yard, etc. I came across a video online that seems pretty simple where they attach a filter at the bottom of the downspout, then connect PVC that runs into the ground and then 90 degrees away from the house underground to about 15' from the foundation (making sure the pipe has a slope to it away from the house). At the end they place a T connector facing up/down. They dug out a "pit" and filled it with pea gravel. The water flows into this. If too much water accumulates too fast, the top of the "T" that comes up right at lawn level has a slotted cover that allows the excess water to drain into the yard.

Has anyone done something similar? Are there negatives to this method (like will the grass look different around the end of this drainage, etc?) The video seemed to take place somewhere up north with dry soil so I didn't know if it would work as well in a poorer drained soil of south Mississippi.

Sorry for the long, rambling post and I appreciate any constructive advice.

LINK