Considering trainer inertia the sudden jumps in the square O/U might
be in fact more demanding than planned for a few seconds in the anaerobic zone which might be critical specially if the workout asks to increase your cadence. I wonder if the triangular shaped O/Us were created to cope with this potential issue
There was a podcast in the past (ep150-185? lol) where they discussed the difference and they boiled down to it didn’t really matter. There are many variants at different amounts of time on the Over vs Under, different % of FTP on the over… etc. There are pros and cons to both - the hard click up to high intensity is a bit more assertive/jarring, maybe a bit more race or MTB like with punches, but some people might like the gradual nature of the triangular.
Either way you will be at or above LT for a period.
Triangle with 1min up and 1min back down is a good gateway from doing 1min Overs… to transition to 2min overs.
ERG definitely will be smoother on the triangle - but is that really ideal or important besides for making pretty graphs? A hard snap to the Above is good stimulus even with the lag at start and end (keep pedaling at end of interval to prevent loss of total time above during the ending lag)
I haven’t found this to be an issue, but I slightly increase my cadence a few seconds before the “over” kicks in. It’s also not a jarring immediate jump in resistance, it’s a gradual increase over a few seconds.
