The principles of flight that apply to flying light aircraft apply in the exact same way to ultralights/microlights.
If one reduces the speed then the controls become less effective.
Aircraft in general are designed with an elevator which will deflect more downwards than upwards. This provides better elevaror control at low speed when one needs to lower the nose (stall recovery) but not the same ability to raise the nose at the same speed (limits the ability to induce a stall).
This is great for avoiding a stall but not so good in preventing the nose wheel hitting the ground if one flares a little high and allows the speed to bleed off.
Many microlight aircraft have stall speeds arround the 35Kt mark but the elevaror looses the ability to raise the nose somewhere arround 40 to 45.
Thus any calculation of the approach speed would better referenced to the speed where one runs out of elevator.
Microlights in general have quite high drag especially at low speed. Thus using a slightly higher approach speed will not have the same problems that it would cause in say a C150.
Microlights also have very little inertia thus;
a) On a normal approach if one holds off at about 4 or 5 feet and then closes the throttle, the aircraft will slow down rapidly and fall to the ground (ouch). Far better to very gradually reduce the power and fly the aircraft all the way to the ground to land on the main wheels.
b) In a crosswind the low inertia makes the crab technique difficult to very difficult. Far better to use the wing down technique from a reasonable height. Then having applied suficient bank to keep the aircraft on the centerline, there is not enough rudder to keep the nose pointing down the runway, the crosswing is too much. Again fly the aircraft all the way to the ground landing on the into wind wheel first. With a strong wind, keep the power on until the aircraft is on the ground.
As to testing the landing carachteristics - make an approach at a reasonable speed and then using attitudfe and power, fly the aircraft along the length of the runway trying to keep the height at about 1 inch to 1 foot above the ground.......never mind if the aircraft touches down....you are at the landing speed anyway. Using this, you can explore the handling of the aircraft in close proximity to the ground and should be able to fly the aircraft at any power setting from full throttle to no throttle keeping the aircraft just above the ground and in a position where a fall of 1 foot will not do any damage............it isn't difficult because we require students to do it before first solo
Regards,
DFC