Mitch, there are several reasons why this method is safer, for once, it keeps the integrity of the glass pane.
There is no need to drill the glass thus avoids any chances of cracking it period.
It eliminates the chance of a leaky bulkhead, trust me this happens more often than I wish and when it happens in a sump is a royal PIA.
Depending on the thickness of the glass it is very easy to crack the glass at the bulkhead when moving the pump just a half inch in any direction while changing, servicing or simply as an accident.
Finally the Sequence reeflo pumps use large intakes from 1.5" to 2" this mean that you will need to drill a very large hole near the bottom of the glass from 2 5/8" to 3 1/4", it is practically impossible to align the pump with the hole opening so you are force to elevate the pump with pieces of foam or wood.