After a year of using XY versions with this new interface I dare to say, that removing
"Boolean logic" checkbox was not a very good idea.
As for me,
more 90% of all my queries are Boolean searches, so almost every time I have to begin my queries with prefix ":".
Entering a colon sign needs using the both hands (pressing shift or moving mouse). Well,
one keystroke or mouse click is not so big trouble and demand as few as 3-5 seconds every time. But if you have to make it 20-30 times per day, and so 365 days it makes... Well I am not able to do such complex calculations at morning, but it have to be very big number

- approx. 5-6 hours of time lost absolutely without any sense.
If you decided to remove this checkbox (IMHO there was nothing confusing with it), you could replace it by some relevant option in general settings, e.g. by a new chekbox
"Use Boolean logic without prefix as default" or something like that and may be the same options for regular expressions and common searches.
In this case you could assign some prefix (point, hyphen, etc.) to to make possible common queries without changing general settings.
Or what do you think regarding showing all quiries variants (common, regular expressions and boolean logic) as a drop-down menu
"Search type" or as three separate checkboxes on the "Find" tab? In this case any new user can see, what types of searches are allowed.