I randomly find the Sorabji 100 Transcendental Studies to be some of his most boring work, and I also find that Ullen plays them like a little girl.
I personally don't recommend buying these.
What is the intended meaning of "randomly" in your first sentence? Do you think the studies to be "some of his most boring work" sometimes but not at other times, at random? Do think think that some of the pieces in the cycle are boiring but others not, at random? A little clarification may go a long way for readers.
As to your view of Ullén's performances of them, I presume that, unless you've heard him live, your experience of this has been from the extracts on his website. Here's another couple of estimations / comments that have been posted earlier today on another piano forum (neither were written by me, I hasten to add):
"Excellent news...well done the fearless Fredrik Ullén."
"I have several of Mr. Ullen's previous BIS recordings, including his two volumes of Ligeti, which included all of that composer's piano Etudes right up through the 15th and 16th, plus many other works (BIS CD-783 and CD-983) -- he's a remarkable pianist! This is a phenomenal project, and many of us will eagerly await each volume through to completion!"
So - each to his/her own, of course - and Mr Ullén would have to be quite the tallest "little girl" that I've ever encountered...
As to the music itself, there are indeed a few numbers from this vast cycle that can fairly be said not quite to represent Sorabji at his very best, but there remains plenty of interesting material within its 864 pages, otherwise I doubt very much that Hamelin, Abrahams and Abercrombie would have spent so much time editing it nor Mr Ullén preparing performances of it nor BIS recording it (although, at the time of writing, much of BIS's time still remains to be spent, of course).
Best,
Alistair