Spellwrought tattoos are similar to the spell scrolls but extremely more powerful.
There's no restriction to casting time, while a spell scroll needs an action to be cast. It doesn't require an action to draw it from your bag or at least doesn't require a free hand to use this. There's no limit to how many you can have in your body, you can potentially have infinite spellwrought tattoos.
Is there some reason to this item to exist? Does this really fits in the game?
You can have a fighter with many shield tattos that gives +5 to his effective AC.
Or you can many absorb elements tattoo and be resistant to most of the kinds of damage in game. With common items which are indestructible. Common items by the magic item price rule of Xanathar's guide to everything has it's price at (1d6 + 1) x 5 gp*.
Spell scrolls has it's cast time bounded by the item. You can't use a spell scroll as a reaction or bonus action because you need an action to read it. What doesn't happens to the Tattoo, which is only limited by the casting time of the spell.
Requiring a hand to use
If you are using a spellscroll of a spell wich doesn't require somatic component, you will still need to have a free hand to cast it as long you need to read it, so you need to have it positioned in front of you, and usually you use your hand to this despite there are other ways to do the same. When you do the same with a tattoo, you casts the spell as if you had it prepared.
Limitation to number held
There is already a tweet from Jeremy Crawford about the tattoos where he says you can overlay a tattoo to another without loss.
Spellwroought tattos are consumable items its base price is halved. So it costs, at mean, 22.5 gp to have access to any first or second level spell of any class. Many of that spells as shield and absorb elements scales wonderfully until the late game. And high level campaigns has a lot of money.
Class and level bounding
Spell scrolls are class and level bounded. You can't cast a spell with a spell scroll if it isn't available to your class. It is also bounded to your magic casting level. You will need to be successful on a DC roll if you try to use a spell scroll which has a spell of a spell slot you don't have access to.
Tattoos don't has any of these limits, the only it has is there's no tattoo for spells from above the fifth level.