Anything selling Shards is a profit only offer.  Even with the weighting (if it exists) there is only an 8% chance of getting a legendary character out of a Sacred Shard.  And they thin'g aren't cheap.

As a fairly new F2P player I find all of these offers atrociously overpriced.

• Bonus Skill Pack (30$): I'd pay 5$ max. Think about it, 350 gems is whatever, 350k silver... nobody cares. 2 legendary books don't do much on their own, especially when a legendary needs what... 10+? 5 epic books is a nice boost, but obviously, they are also easier to get. I'm not going to spend 150$ to fully book a legendary and maybe 2-3 epics.
• Mini Mix Pack (15$): I'd pay 2$ max. 2x clan boss keys, chickens and 2x ancient shards are mediocre at best. 30 xp poitons is kinda meh. 1.000 energy and double xp is useful. 1.2 mil silver can be quite easily farmed.  7 arena refills... nobody in Bronze and Silver cares.
• Speed Set (30$): I'd pay 2$ max. Probably random main-/sub stats and if not, gear can be farmed and you need a lot of it. Worst of all, it's not even 6* gear. 650k silver useless, 500 energy is almost the best thing about this offer. I mean, all this speed set does - if you are lucky with stats - is to gear a single hero, that's not worth 30$.
• Sacred Founder Pack (50$): I'd pay 5$ max. Sacred shards are overrated. I mean, you have a 6% chance outside of x2 events. Even with 10 of them, you have a 53.86% chance to get no legendary (27.85% during x2). I'd rather have many ancient ones and get useful rare/epic heroes. 5 ancient shards can be easily obtained by simply playing the game. 5 rare books is probably the best part about this offer. Who cares about 1 epic book, 300k silver and 500 gems? They are just added so the offer doesn't seem as bad/empty as it is.

In terms of offers being overpriced

• Bonus Skill Pack (30$): even 10$ would be kinda overpriced.
• Mini Mix Pack (15$): should be 5$.
• Speed Set (30$): anything above 10$ is overpriced, 5$ would be fair.
• Sacred Founder Pack (50$): 10$ would be quite expensive but somewhat fair, everything above is completely overpriced. 

But since people, for whatever reason, blindly buy these offers, they won't get any cheaper. I'd be willing to spend some money, and I regularly spend 5-20$ on mobile games, but these offers are rip-offs. 

1. Avoid ALL offers, they are ALL over-priced
2. Have patience and play the long-game.  99% of the time the shards will disappoint you.
3. Enjoy the strategy of working with what you have