The Martelli cutter is a great option to think about. It is an ergonomic design that really does do what it it is promoted to do. It relieves the position of the wrist and arm that causes repetitive motion problems - i.e. carpal tunnel syndrome, tendonitis, tennis elbow, etc.
Those who already have these problems may find that they can cut again and for longer periods of time without aggravation.
The time to learn a new way to hold the cutter is a short learning curve and worth it in my opinion.
The replacement blade issue is that some rotary blades have an irregular small inner circle instead of smooth that can damage the 'stem' that holds the blade in place on the cutter. If the small circle is smooth, it doesn't have to be a Martelli blade replacement on the 45 mm. The 60 mm cutter does need a Martelli blade.
I do not work for the company, lol - I asked all these questions at a Martelli demo at a large Quilt Show.