Credit building products!

Which is the best and most effective credit building product, that’s not a credit card.

Ones which I’ve come by:

Portify (offers interest free lending)
Bits
Loqbox

How impactful are these services?

Some of the services offer higher tariffs, claiming that they offer greater impact to your score.

Does it even matter if your supposed credit limit is £1,500 Vs £200. I thought what matters is that you pay either on-time or in full and don’t utilise more than 50% of your credit limit, not the limit you’re given. If that makes sense!

Any insight into this would be helpful!