Are NCLT Coins Really Legal Tender?

Australian NCLT coins are legal tender and banks will cash them in at face value. Every Australian coin, except holey dollar and dump (which have been demonetised)is legal tender.
That means banks should also cash in pre-decimal but you might find a reluctance there if you tried it.
They certainly do cash in 1¢, 2¢ and 1966 round 50¢. I have often been able to obtain those from banks -paper notes too- saves them the trouble of packing them to return (minimum quantities apply for that).

The rewards points scam would not apply in Australia because NCLT issues are sold at a premium to face value.

Edit P.S. I have also occasionally been able to get $200 gold coins this way too. They are worth around double face value.
Many bank tellers now know the value of some of these coins and will buy them for themselves.

The core problem is the "buy $20 for $20 in bulk, we'll even throw in free shipping, you can pay by credit card" attitude some modern mints have adopted. This leaves them open to credit card points-skimmers. While I have little empathy for the scammers, I hold the Mint ultimately to blame. They should never have combined those three things. Either "buy $20 for $25 each", make them pay for shipping, or refuse credit card transactions. Any one of those would break the cycle and ensure that only coin collectors and speculator-investors buy the coins.

As for "legal tender", that's defined by law in the country of issue. These British coins are still "legal tender" in Britain, in terms of: you can still pay your taxes with them, and you can still use them to offer as payment for a debt. So if the bank charges you a fee or calls in a debt you owe to them (such as a loan repayment or credit card installment), you can pay the amount owed in these coins, and the bank would be obliged to accept them, as they have been tendered in payment of a debt.

Further, the memo sent by the Mint to the banks was completely out of order. It is, frankly, none of the Mint's business what people choose to do with their coins once they are issued and sold. It is the Mint's stupid marketing decision that created the problem (as outlined in the first paragraph), they should bear the cost of solving their problem. And sack their marketing department, if they're looking for a scapegoat to blame.

From the Australian perspective, very few NCLT coins are or were issued for face value. The early $5 coins such as 1988 come to mind. There were also some near-face-value precious metal coins that became de-facto face-value NCLT when the price of PMs collapsed back in the 80s and 90s. The silver 1982 $10 and gold koala $200 coins come to mind.

In all cases, the banks in Australia happily accepted them as deposits and returned them to the Mint, though some, perhaps being stung by counterfeit NCLT being deposited, put policies in place not crediting your account until after the Mint had verified that the coins were genuine. There weren't enough people depositing NCLT for the Mint to consider it a major problem. The RAM and Perth Mints would be very, very foolish to attempt to imitate the RCM and Royal Mint in this regard.

I had one date with a guy who used $5 coins to pay for the date. I was flabbergasted and needless to say we only had one date. He was truly an idiot.
(I was a broke teen, otherwise I would have bought them off him.)