If an employer wants you to have a (as in any) TEFL certificate, this one is fine. If they want you to have taken a TEFL course which includes the all-important assessed teaching practice, then an online TEFL certificate from i-to-i (or any other online provider) will not suffice. There is a big difference between the 6hrs of assessed teaching practice on a CELTA or equivalent, where you are teaching real students, and the weekend/classroom element of an online course, where you are teaching your fellow trainees.
If you can't afford to take a CELTA or Trinity CertTESOL, either from a cost or time perspective, you can take i-to-i's 140hr online TEFL certificate and then pay an additional fee to take their new EDI CertTEFL. It is a Level 5 qualification and as such is equivalent to a CELTA/Trinity CertTESOL.