I've ordered plenty of stuff
directly from Smyth's website, without any extra charge. Oddly, I can't find anything online about additional charges when accessing the site via Facebook. (Even if Smyths weren't very open about their policy, I would have expected to see posts from other people complaining about it). Smyth's definitely use a Facebook tracking cookie on their website though:
https://postimg.cc/7Gckq9KP
My only problem ordering online with Smyths has been when I've used their click-&-collect service and been misled by a text stating "Your order is now ready for collection". I'd ordered a product which required batteries, plus the batteries to go with it. I got both an email and a text advising me that I could collect my order and therefore didn't bother to open the email, assuming that they both contained the same information. If I'd have opened the email, I'd have seen that (contrary to the information on the store's website) the product was out of stock and therefore that the only things awaiting collection by me were the batteries for it. (The text failed to mention that!). So I had a wasted journey.
Sadly now though, with the youngest recipient of presents from me about to become a teenager very soon, I'll now no longer have an excuse to buy all of the toys that I would loved to have had myself :(