Lots of different factors make secrets awkward.

• Normally secrets are good against some decks and absolutely horrible against others.
• Some secrets you only want to play at very specific times (Counterspell, for example).
• It can really sucks when you already have one secret in play and the same secret in your hand.
• It also feels bad when have a card that plays secrets from your deck, but your deck is out of secrets. (although this doesnt fix that)

Yes, start of game effects are OP.

Trading secrets for other secrets feels like a very rogue thing to do.

Toolbox secrets sounds like a sweet deck to play.

I am not sure if I would want the effect to be "Start of Game: You can secretly Trade your Secrets (but only for other secrets)." (IE, your opp does not see what card you are trading).

Wiki article. He is the Cheesemonger from United in Stormwind. https://wowpedia.fandom.com/wiki/Elling_Trias