You won't spare a click to install the card since you paid a click to host it anyway.
When played it gets you at -4 (3 credits + a click).
- 1 card installed gets you to -2
2 cards installed get you to 0 ... so The Supplier is useless thus far
3 cards installed get you to +2 ... Infiltration and Easy Mark are better
4 cards installed get you to +4 ... better play Hedge fund
5 cards installed get you to +6 etc... 1 CE better than lucky find
From 5 cards installed with The Supplier (which means 6 turns of play), it gets interesting.
- When The Supplier is trashed, you lose X clicks, X being the number of cards hosted when trashed. So make sure you won't get tagged.
So it is only viable - but very efficient - in a big connection deck. I agree that Iain Stirling is the identity that can use it best.