In the case of making a small claim (where it is a monetary claim under 5000), it may have more weight than a lawyers letter (as you are effectively suing them at that point), and they will then be on the hook for settling the filing fee as well, whereas you would otherwise be paying for a letter from a lawyer (although sometimes that cost could also be recovered through the small claims track). You just need to make sure you follow process (28 days notice, etc - again just contact ECC-NET to be aware of the correct process).

Of course, there are occasions where a lawyer may be needed (just as there are for domestic disputes), but being aware of your rights in advance will let you know if you have grounds without the need to pay a lawyer for consultation.

Also worth pointing out again that your EU consumer rights are identical for domestic and cross-border disputes - but for domestic disputes, you can contact your local consumer protection agency instead of ECC-NET as you may have MORE rights domestically (higher small-claims limits, for example) - although i expect ECC-NET would simply refer you in such a case