Is there a reason to buy shields from Russ?

In the Eldin Canyon, north of the Sheh Rata Shrine, there is a shield salesman named Russ on top of a hill. He says he is part of a shield surfing gang and has three shields available to buy:

• Wooden Shield (30 rupees)
• Soldier's Shield (100 rupees)
• Knight's shield (300 rupees)

According to the Zelda Wikia, Link can only purchase each type of shield once. Once Russ sells out, he is not able to restock any of his shields.

If you examine a shield and say you don't want to buy it, Russ laments that if people don't start buying shields, his shield surfing gang will go out of business.

Does something special happen if I buy all three shields? Or is there some other reason to buy shields from Russ?

There is a Korok seed race platform top of the tree next to Russ. The timer is too short run or glide. Russ's comments hint that shield surfing, a faster form of travel, should be used.

Should a player not have a shield or break theirs in an attempt to shield surf, three more can be bought from Russ.

Additionally, if you buy all three shields, Russ will tell you where to find a Hylian Shield.

Oh! Speaking of not breaking, have ya heard about the Hylian shield? Everyone in the surfing scene covets that bad boy.

It’s clearly commissioned by the royal family or somethin’! Its sturdiness makes it perfect for shield surfing too.

You don’t really see ‘em around these days... but rumor has it there’s one in Hyrule Castle.

If you buy all 3 shields, he thanks you and tells you this:

The legend of the shield-surfing world is Selmie! When Selmie boarded a shield, nothin' could stand in her way.
Everybody who saw her tear it up was practically hypnotized! That's raw skill, man.
She retired young and became a living legend. They say she settled down in the Hebra Mountains to the northwest.
If you're serious about shield surfing, maybe you should try to track her down.
(Actually, lots of folks have tried to meet her... And they all ran into trouble along the way)

Selmie is the shield surfer you meet up in Hebra Mountains. You can pay her to train you and do her courses to get nicer shields if you beat her time constraints.