I have been thinking about this for awhile. Mainly because I came back to the game with the avatar feature already being unlocked. I remember it being the FIRST thing that I really wanted to get, because it individuated my account. In those days, your avatar did not get sent back to the vault after inactivity (otherwise I'd have a really cool avatar, I don't remember it, but it must have been really cool).
Something I realized while playing on my alt is that it is hard to get to the avatar option (unless he's been buying in the wrong category...). He has spent probably 11 credits with the sole purpose of moving through unique features to get to the avatar option. He still isn't there. Granted he has hasn't spent any money yet.
This is important because choosing an avatar is one of the greatest ways to increase fidelity of a player to a game. To make that player invested in the game. I literally helped a friend write his Master's thesis on this. In his experiment he had taken a basic MMORPG game (with the help of some coder friends). He had (I think his n for each group was like 30) 30 people play the game without selecting an avatar, and 30 play with selecting an avatar. I can't find his published thesis. But I do remember that he got statistically significant results that the people who selected an avatar answered the survey saying that they were interested in playing longer. Now I think his alpha was .05, so it was a typically lenient study. However I think that says a lot. Now, since I couldn't find his study, and I don't have free access to psychology journals anymore, this is the only study I could find. https://cyberpsychology.eu/article/view/4340/3412. It supports the same hypothesis from my friend's master's thesis. Though we can draw multiple other conclusions from the results of this study, such as perhaps letting players choose their border (such as Chewett unveiling the old "dark border" might actually be worth an investment, ie letting player's pay in shop for changing color schemes might actually be something people would want <I really think they would want this, if for no other reason than their screenshots look different from everyone else's>)
Now all of this to say is that I think that when players unlock that 5 credit bonus on GI, that an avatar should be one of the first things they should get. No, I don't think they should unlock it within that 5 credits. But I think having it be one of the things they can SEE at the bottom of the page and it plainly says "Avatar" on it (I don't know because I still have yet to unlock it) might give them something to strive for. Then they might either use free credits (which helps the game even if they quit), pay (same outcome but better), or do both and keep playing (obviously the better outcome). Putting the avatar option in sight might be a good choice.
TLDR: Move Avatar option up in shop so new players can see it, not buy it at first. Click the hyperlink, scroll down to the conclusion section of the paper and see why. Answer the poll as well to see what MD community thinks. If you select other, please explain in your post why. Better yet, explain in a post about your choice regardless, give voice and more depth to your answers.
If you have some kind of disorder and a wonder cure appeared, a miracle pill or something, would you care for why and how it works for your disorder? Would you like the miracle to exist and be happy that your pain is no more, or would you seek the explanation for how it does what it does, even if you might find out the truth you dislike, a reality you'd resent?