F&F accepted I think - wording advice

Evening,

Back once again for some advice on behalf of a client (same one you helped with last time, a SB letter was suggested, and it worked, so thanks!). Offer has been made, and accepted using NDL F&F letter. Just wondering if you could check the wording of the letter received to confirm if this is watertight or not? The creditor has used the term 'partial settlement' not F&F so it's made me unsure:

'We write regarding the above account and further to your letter in which you made an offer of [X] as a partial settlement...blah blah blah about how good their customer service is blah blah...

We are willing to accept your offer of [X] partial settlement. Please confirm when you would like to pay this amount.

Please note that if this appears on your credit file it will updated to partially satisfied, however the outstanding balance will show as zero and you will not be pursued for any remainder of the balance....blah blah blah abouthow this may be viewed by other creditors and details on how to get in touch with them'

It's not on their credit file any more and the settlement is a 1/3rd of the total amount owing.

Is their wording watertight enough? If not, how to proceed? If it is acceptable, is it advisable to write a covering letter when posting the cheque reiterating that this is a full and final?

TIA once again