The biggest problem I see other than concern over the strength of the handle (which would be easy to fix — and I would round it off during redesign), is the number of different versions you would need.
First, there’s the left and right hand models. Due to the shape and use of leverage (fingers pull up while lower hand pushes away on the handle), you would need one for each handedness.
Then, you can’t make an assumption that bigger handed people drink more coffee and smaller handed people drink less. But to scale the handle you have to either scale the cup into sizes, or have one size cup with handles in XS, S, M, L, XL like glove sizes. Hand-fit is important for leverage and comfort.
Multiple sizes requires more shelf space in the retailers that sell these and in the cupboards where consumers keep them.
Steal this solution so you can steal this business: Spin the problem into a marketing win. The consumer is buying a very personal item made just for them. When you buy the mug, you get a code that you can use in an email, website, text, etc., to send in a custom picture. The customer can send their name, artwork, picture, avatar, or anything else and receive a custom sized, correct handed, and personalized mug.
The store versions are all right handed, Large models that can be bought and used immediately, or handled by the consumer to facilitate the purchase.
Bonus: Change the name to something that says its personal, better for holding, or leads to better tasting coffee — “Muglove”? You can do something with the font and logo to show not only is this “Mug Love”, but also a “Mug Glove”.
Which is good, since the current logo looks like a cheeseburger. Make the logo a picture of a hand grabbing and tipping the mug, which implies it’s a glove while also showing the proper way to use it.