Tell is a character who maximised his screentime. Although he is only a side character in LB4 and has not gotten any spotlight beyond LB4 and his own interlude, it is enough to make him a compelling character.
We learned he is uneasy with the Assassin-like properties in his lore, which looks like a convincing justification for his third append skill to be against Assassins.
It is also interesting to see him stack up against other legendary hunters. Tell has neither Orion’s archery skills and brute strength, nor Atalante’s instinct and finese, but he managed to out-hunt them both through patience, composure and better compatibility with the scenario.
The interlude ended with a reminder why he is a heroic spirit:
The interlude explained William Tell as a heroic spirit: he is not strong or extraordinary by any quantifiable metric, but in the right scenario and environment he will pull through with his composure and experience as a hunter and a father.
If you are a poor mage who cannot sustain more powerful servants and got roped into a HGW that is to be fought in the mountains, Tell sounds like a pretty solid servant to summon.
Of course, I greatly enjoyed the Yagyu cameo as well. His dynamic with Tell and Nobunaga adds more to all three characters. Nobunaga called him cunning for seemingly setting up this hunting session with the three of them, meanwhile Yagyu seemed to just be just having a fun time hunting with two people who interested him.
An interesting translation trivia concerns Nobunaga’s ‘Munerin’ nickname for Munenori, in JP when Nobunaga addresses Yagyu the text looks like this:

The big kanjis are ‘Tajima-no-kami’, while the small katakana above it reads ‘Munerin’. This trend of occasionally putting small letters above a phrase is a quirk of JP which to my knowledge is not carried over to NA at all.
In the NA text, she straight up calls Yagyu ‘Munerin’ in this interlude.
I interpret this JP quirk as Nobunaga actually addressing Yagyu properly as ‘Tajima-no-kami’, but nicknaming him as ‘Munerin’ in her mind. Obviously this subtlety is lost in translation since NA does not do this small letters thing.
Though the next time Nobunaga and Yagyu appears together in an interlude (Vritria’s interlude which obviously is not on NA yet), she directly calls him ‘Munerin’ with the nickname appearing as big text instead of small text hinting that the two are growing closer.
As I said, minor translation trivia, but these sort of things interest me and I have been tracking Yagyu’s numerous cameos outside of his main story roles.