I own several onaholes. It's a good cope, but you have to innovate to keep it interesting, which means progressing to the next tier of items every once in a while, or else the hassle of having to clean and dry them slowly starts to outweigh the extra pleasure that you get from using them. I don't have the balls to make the jump from hip-sized holes to a torso or a doll, so at this point I only use the stuff that I have once in a blue moon.
Some tips if you want to get into it:
-Start with the small holes (200-500g). I recommend buying two right away, one made of soft material and one with standard material. Once you get the feel of what you want out of the material in terms of softness, you can go for larger, more expensive types (500g-1kg).
-Don't be cheap with lube, get at least two different types (one thick one standard or runny).
-Avoid buying gimmicky types (blowjob holes, nipple penetration holes) as your first.
-Don't get fooled into thinking that the tunnel's shape is the most important thing - it isn't. Material, size and arguably tunnel length have more impact on your experience.
-Tunnel depth should be similar to your dick length, it feels great when you can comfortably go balls deep while bottoming out at the same time.
-I definitely don't recommend going straight for dolls. It's much better to learn about your preferences as well as the basic maintenance on smaller and cheaper toys.