Fuji,
The problem with pilots doing extra checks is that they end up as words without actions.
Even a display pilot would not claim that every manoeuvre is without any posibility of not working out as planned.
Problem is it seems that for your aero sorte, the H - Height is simply that you start at several thousand feet. For many others, Height means start height, manoeuvre heights, top and bottom, minimum height over the top, end height, authorised minimum, obstacles and no go areas.
Location includes start point, display line, wind effects, end point, escape routes, avoid areas.
Lookout means checking that the display box (or practice box) is clear and is a continuous process not a "I'll do a 360 and if I don't see anything then I can blast away"!
A proper HASELL check is not simply a check of current situation but a review of future situations and limits.
Perhaps the most frightening thing about flying a steep turn is that some prat who is in the overtaking position will be doing a stupid barrelroll (thinking it is an aileron roll) and not paying attention to what they should be doing in that position.
The closest Airprox that I have had was when I was straight and level in good VMC at a constant height in a well contrasting aircraft. The other aircraft overtook about 30ft above the cockpit. Flying in straight lines is far more dangerous than manoeuvring. Movement catches the eye. Moving the aircraft round makes it more visible and if it is visible then pilots will avoid it!
Regards,
DFC