In the wave energy conversion field, simulation tools are crucial for effective converter and controller design, but are often prone to become very case-specific, in both structure and parameter selection. This is due to majorly different working principles and diverse importance of nonlinear effects, at times requiring ad-hoc modelling approaches. To tackle this challenge, WEC-Sim (Wave Energy Converter SIMulator) was born from the National Renewable Energy Laboratory (NREL) and Sandia National Laboratories, providing a unique simulation platform for all WECs. Nonlinearities related to time-varying wetted surface, especially important in floating WECs, are included in WEC-Sim through a mesh-based computation of nonlinear Froude-Krylov forces. Virtually arbitrary geometries can be considered, thanks to the discretized representation of wetted surfaces, at the price of a significant increase in computational burden. This paper considers a time-effective alternative, implemented in the open-source toolbox called NLFK4ALL, applicable to the popular and wide family of axisymmetric floaters. The Spar-buoy floating oscillating water column device is considered , particularly challenging due to a submerged volume composed of several different sections. The accuracy of WEC-Sim and NLFK4ALL is verified by a preliminary cross-comparison, using independent methods to compute virtually same effects. Fixed-body numerical experiments are used to quantify nonlinearities and compare not only the accuracy, but also the computation burden. Results show that both methods provide almost identical results, although WEC-Sim doubles computational requirements.