The phrase "challenging but interesting" is correct and can be used in written English. It is typically used to refer to a task, activity, or situation that is difficult, yet rewarding at the same time. For example: "I find my new job to be challenging but interesting - it's a good balance that keeps me engaged."
HCW found it challenging, but interesting, to collaborate with families with obese children.
"That makes it challenging but interesting at the same time for us as a business.
One of the most challenging but interesting compatibility requirements is the need to support the verified presence of frame rate variation.
How to design a synchronization controller when the master system's states are unmeasurable is a challenging but interesting work.
Challenging but interesting classes or sports can become hobbies.
With a limited $25 budget, it made this tasks to be more challenging but also interesting.
It is typically more challenging but more interesting than something you would find in typical textbook English.
The associated constraints can be a challenging but very interesting and rewarding starting point for architectural design.
The results reported herein clearly demonstrate that the aerosols generated from both products are not the same, and this makes testing them in vitro challenging, but also interesting and insightful.
More challenging, but more interesting.
Most of the respondents rated the management of the children as 'challenging' and 'challenging but interesting' regardless of their age group and number of years post graduation.
Being a terminologist, I care about word choice. Ludwig simply helps me pick the best words for any translation. Five stars!
Maria Pia Montoro
Terminologist and Q/A Analyst @ Translation Centre for the Bodies of the European Union