[martinkrivosija]

It's definitely no secret but those testers do not provide the full story. No do IP blocklist checkers - not all blocklists are created equal, nor do most have any impact at all.

For most senders, whilst IP reputation does play a role, as long as you're on a decent platform the majority of your deliverability concerns will be surrounding your own domain's reputation. Your domain reputation is directly influenced by your sending behaviour. You need to be sending to people who want to receive your email and will engage with it.

iamacyborg's response above is spot on.