I really like Low Whistles and I play them much more often than high whistles.
I owned and played a Burke Low D for a couple years. It has strong volume and a massive booming Bottom D, which is great for playing in the old-time wooden flute style (which many Low D whistles aren’t capable of).
The drawbacks which lead to me selling it were, first of all, a large appetite for air. In other words a large volume of air passes through the whistle while playing, especially in the 2nd octave, meaning that you have to take breaths more often. This isn’t an issue in the old flute style I mentioned, where frequent breaths are often part of the style.
The other issue was the Burkes in general have larger tubes than other makers, with a given size. That fat tube combined with a relatively wide finger-stretch made the Burke not optimally ergonomic for me.
Many people dislike the tone of Burkes, calling it bland, but for me the tone wasn’t an issue.
I owned a number of MK Low Ds and played them for several years. For me the MK is more ergonomic (narrower tube and closer finger-spacing) and the MK is far more air-efficient. The MK’s tone is unique; dirty and complex. Some dislike it, but I love it.
But for me the best has been the Goldie Low D: exceptionally ergonomic, great air-efficiency, nice tone, great tuning, everything.
I consider all three of those to be serious professional instruments.
The most ergonomic entry-level Low D I’ve tried is the Dixon all-plastic conical-bore Low D. Its narrow tube, close finger spacing, and small air requirements make an ideal introductory Low D.