'rather difficult to understand' is correct and usable in written English.
It can be used to describe something that isn't easy to understand. For example: "The professor's lecture on quantum mechanics was rather difficult to understand."
As a consequence, it is rather difficult to understand, assess, and compare the existing approaches.
Unfortunately, it is rather difficult to understand all the subleties and for that reason we propose to couple EQCM measurements with inductively coupled plasma (ICP) analysis.
However, conditions just aren't quite how Adrian imagined in his youth; he hasn't managed to pursue his international poet idea... Overall this book was rather "all over the shop", as it contained different sections of storylines compiled together, making it rather difficult to understand.
Given that Ronaldo and Messi combined have won the prestigious award for the last six years (Ronaldo won his second on Monday to add to his 2008 crown while the Argentinian has taken the last four awards), Kompany's opinion that neither have been better than the three he chose is rather difficult to understand, although there is a case for Ribéry after his treble-winning season.
Since the visualization of a GMM modeling a three-dimensional histogram is rather difficult to understand, Figure 8 shows two GMMs modeling only the histogram of the green color channel of the car in sequence Parking_lot.
Several residuals have been proposed, but unfortunately most are rather difficult to understand in the context of survival analyses due to censoring (Collett, 1994).
Still, it is rather difficult to interpret.
Multiple scenes in the episode were meant to be rather confusing and difficult to understand in order to interest viewers so they would watch the episode multiple times, trying to learn something new each time.
The most important point which stands out from this IPI is that learners focus more on specific sections of the video which contain concepts that they find interesting or difficult to understand, rather than the entire video.
While this is useful, my main caveat with this feature is that text notifications are cut off after a rather short character limit, making it difficult to understand longer texts.
What renders "Mother!" somewhat difficult to understand isn't its complexity but, rather, its simplicity.
