...the fact that there's oodles of time between leaving the dock and arriving at the site to get ready. If you're not doing it, something's wrong and it's not your configuration.
Depends on the boat and the speed you are going.
A small speedboad requires you to load prepared equipment.
We should always remember how very slow beginning divers can be, sidemounters tend to repeat that.
They can't get their inflation hoses connected, forget important equipment, take a long time to leave the surface after jumping in...
In new sidemount groups there is often a lot of unintelligible yelling while drifting at the surface, often individual beginners break off the dive and get back on board...
The same happens when new groups with inexperienced leaders do their first backmount boat dives, but most problems can only be solved on the boat with those groups and group leaders understand the equipment and can help.
Sidemounters can look very disorganized in contrast, constantly fixing something or another.
Dive leaders often do not understanding the equipment of individual sidemount divers or buddy teams tagging along and cannot look for mistakes during setup.
I think it very important to really consider the details of the situation for comparison.
When you really compare individual steps sidemount proves it's effectiveness in theory, in practice individual divers often fail at some small detail.
Sidemount needs people to develop procedures for many situations and boat diving in particular is severely underdeveloped.
I was on a safari boat also offering sidemount-only safaris.
Crew and guides where about as much help as a purely backmount experienced crew - knew nothing, even less than crews I had met before.
Just before the last planed zodiac dive, however, someone recommended not clipping into the backward hip D-rings while sitting and climbing, but the forward ones.
Perfect solution! Something impossibly hard became manageable in the blink of an eye.
If we had those procedures sorted out, sidemount on boats would be a great experience for everybody, until we have and people can get access to that information however...?