I ran a roofing company for several years (we also provided seamless gutters), and I have seen just about everything that can happen with gutters.
The working premise behind the gutter guards is to prevent leaves and other debris from getting into the gutters, typically accomplished with small perforations to permit water to drain into the gutters while keeping the solid stuff out. Some are better than others but they all share one shortcoming, and that is the fact that the water draining through will carry with it any dust, dirt, and small pieces of decomposing vegetation. Over time this will accumulate in the gutters, particularly in any low spots and around downspout drains. The result is essentially a mulch bed. Depending on actual content the accumulations may be anything from rock hard to loamy soft. On many occasions I have seen vegetation sprouting and growing in gutters.
My point is that the gutters will continue to require regular cleaning, with or without gutter guards, and that cleaning is a lot easier to do without having to remove and replace the gutter guards every time.
At my house the gutters are installed with some pitch to drain to the downspouts, and there is at least one downspout for every 20-25 feet of gutter. I clean them out every fall and every spring, first with a putty knife to remove any debris, then with a pressure hose to flush everything thoroughly and clear the downspouts.
YMMV.