I didn't even know that Riot had even made this feature available. No post explaining it in News, no in-client messages, nothing. For something that many people have been eagerly waiting for since the patch came out, this is incredibly unceremonious.
As for the splash arts? I think they messed up. Very few of them are centered, being too far to the right and usually being obstructed by the search bar. This leaves a lot of empty space on the profile, along with the shadow. I wouldn't mind that shadow so much if the characters took up the space that they should, but as of now, it just seems unfinished. Now when you hover over your icon in the top right, the profile splash looks way better, and many of the splashes have been tailor for that position, being centered and, for the most part, whole.
Then there's the fact that you have to open the window to change splash arts every single time just to see and choose which one you want. And now that you need to find one that actually looks good and centered, it's even more of an issue.
Do I like the feature conceptually? Of course. But do I like how it's being done right now? No. I don't know how hard it would be to center the splash arts better, but even if it takes some more time, a fun feature like this could use the extra polish to look it's best. Though this is all my personal opinion about this, for a feature this nice and one that I had been waiting for, I needed to at least get my 2 cents out, for what they're worth.