In some cases, what's offered is just to "see the content in advance", rather than "see the content" itself.
In other cases, the patreon version differ in some point to the public version or work in progress images are added there.
In most case it's a mix of the three categories, depending on the artwork and number of versions that were drawn.
No big deal here. At best you'd probably be missing on early sketches and tiddies that may aswell have fur over them like in the family friendly design everyone knows and like; or see some pictures a few days/weeks/months late here with the exception of the kind of alternative versions mentioned above.
That's how patreon works, with each artist being free to set their own policy no matter if the norm tend to go toward exclusive content.
And we're kinda lucky that some goes to the lenghts of still showing stuff for free, because if everyone was locking the paywalls as soon as they get a big enough fandom many series and artworks would fall in a closed fandom fading into obscurity scenario.
So...Yeah, the content is free here and there's a reason for that. That the artist is a nice guy or just promoting their stuff (since after all, Twokinds is an ongoing webcomic you can read online or buy tomes as they get completed) the conclusion is up to you.
All of Tom's art is 100% free and available for everybody, save for a few side comics and the physical art book, and even most of the side comics have later been released for the general public. You don't have to be a patron to see most of his Patreon art, only pieces like this that Patreon deems too "adult" for people to see without paying, which is why he puts them here on DeviantArt, instead.