Lip Tars...about the only con I can think of...they bleed. Here is a simple step by step that you can follow so that you won't get the bleeding and mess.
Squeeze a TINY bit onto your fingertip (think half a pea size)
TAP in the product with your fingers. Don't spread it with a lip brush. The reason why you might be getting the bleeding is because spreading it causes it to SIT on the lips. When you tap it into the lip, the lips are absorbing the color (kind of like a lip stain). If you're having a hard time getting the lips lined perfectly, you can use a lip brush after tapping and using ONLY the product that is already on the lips. Adding more product will cause it to bleed and become messy.
FINISH: Matte / Satin
Use translucent powder to set the lips. This will keep the tars from moving around and creating that bleeding effect.
Step 4 (optional): The reason why step 4 is optional is because it doesn't HAVE to be done but it all depends on you. For extra reinforcement of the tars, put some concealer around the lips and blend.
You can follow up with the gloss of your choice if you want to go with a glossy look or keep it matte depending on what look you're looking for.