I think the OP asks about first hand experience with the slightly larger US sized carry-on trolleys that are customary in the US but in principle are too big to be allowed as cabin baggage with many/most European carriers, including Ryanair.

No first hand experience, but after several Ryanair flights and experiencing how this is dealt with at the gate of Ryanair flights, there is a very good chance that the gate agents will not notice anything if you bring a trolley that is 24cm in depth rather than 20 cm. The difference is insignificant and hard to notice. However, you definitely will have to purchase the "priority & 2 cabin bags" option in order to successfully bring a carry-on trolley onboard (regardless if US sized or "European" sized). As mentioned above any pax with a trolley (but without having purchased the priority queue option/full carry-on allowance) will most likely be singled out and requested to pay for excess lugagge at the gate (then it is much cheaper to buy the "priority & 2 cabin bags" option in advance).