Halifax Clarity Card? BEWARE!

The credit card is HIGHLY unreliable, because Halifax puts random fraud prevention checks into place. As I have been told, they are not foreseeable, as otherwise they can be circumvented. So the credit card may or may not work ... with awkward consequences.
My story: Arrived at Austin Airport 6 days ago and tried to withdraw 300 $. The money was not paid out, yet, as it turned out, I was billed. I could withdraw 200$ afterwards without problem. Called Bank of America (EE charges 1£/min roaming) who told me I had to phone Halifax. Halifax will send a claim form, which takes ANOTHER 7 days to arrive, whilst Halifax charges cash advance fees!
Today, I tried to make a bigger purchase (> 300 $). Card declined. Shop assistant tried couple of times, even with paying partly in cash to reduce the amount: declined! People were looking; I left the shop to phone up Halifax (battery low, because I used my phone all day, and needed it to find my way home. Very uncomfortable feeling) ... finally  transferred to the right department: Fraud detection. Be prepared! You need a pen for the case reference number or you have to give all details again. Had to answer questions like 'How long have you had the credit card for?' 'How many accounts do you have with Halifax?' 'Approximate balance?'. If you don't have online banking at hand it is difficult to tell at the end of a month when all the bills go out!
Finally security clearance, block lifted. Went back to the shop, apologised for the hassle, reassured that things are straightened out now and tried to pay again: Declined! Shop assistant tried combined cash/credit payment: Declined. The shop assistant had to return the good to its place. I apologised again and promised to come out tomorrow (takes only 30min one way) with ALL my cards to make sure that at least one works. I felt humiliated to the bone.
I phoned up Halifax again... same procedure. This time I was asked to name a street in 1km radius from my home address, different from where I live. Not easy for me, as I was fuming and don't really pay attention to that (SatNav). Explanation this time: Another security level had kicked in and was imposing a second block!
There may be more blocks, I don't know. It can not be managed from the Halifax app, so even internet access doesn't help you. You need to phone up (I was in total 20min on the phone to Halifax today!)
If I had had another card with me, I would have paid with it... which begs the question: What's the point of Halifax Clarity? The frustration and the phone charges do not make up even for 3% foreign payment charges.

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Wrap up: To use the Halifax card, you need another card or
- a phone with low roaming charges
- a pen or else you stay longer in the line.
- be prepared to answer a Jeopardy quizz of questions.

It is not guaranteed that you can pay, after that.