Full and Final with one of the lenders

Hi all
I have been on DMP for about 3 years. I have been seeking to get a full and final settlement and have finally been able to negotiate my first settlement with one of the lenders DC called CapQuest at around 50% of loan and I am happy with the offer. They have sent me letter as below:

Thank you for your recent contact with this office.
We confirm the a full and final settlement has been accepted for the amount of £xxxx.xx and is due on the xx of 2017

Please be advised that the amount paid to settle your account will be less than the full outstanding balance, your credit file will show the balance as satisfied with a special flag of partial settlement.

On receipt of payment the account will be closed and you will not be pursued for the remaining balance.

I hope this letter above should now be OK for me to arrange a payment for them. Does this look like they have covered everything legally, that I needed, to make sure they will not come after me or sell the remaining balance to some other DC.

Should the partial flag on default in the credit file be of any worry? I am not worried about getting the defaults removed from me credit file as I am "hopefully" never ever going to borrow money again and the default will disappear from the credit file after 6 years anyway.

One slight worry is that is it Ok to negotiate with just one lender and not will all?

Thanks