It's better to use grammatically correct and conventionally accepted statements.
Beginning a response with "I agree" or "Good point" reads pleasantly, without the nails-on-chalkboard effect of the internet-nerd-herd-mind irritating-and-head-scratching-to-regular-people nerd-convention of "This".
Stupid nerds. They seem to like to demonstrate how "non-conforming" they are, but reading sites like this, or worse, reddit, shows how readily they imitate one big nerd group.