If you use it for alignment or more pro uses that requires strictly the beam divergence or beam diameter in certain distance, the PIONEER 300mw-600mw green lasers, featured with the lowest beam divergence and intensest beam power, is the best choice. PIONEER SERIES model is the most cost-effective one and have all high-end functions and the structure is made strictly according to the FDA 5-point system, and the outside or inner structure and dimensions are all FDA-certified. Toplaser-II series is more inexpensive and works well, and the beam size is kinda bigger than other models, and Yamataka series's too bulky and not easy to carry. Volunteer series takes 2-5 seconds soft-on delay, and needs 20s to 1 min's warm-up time to reach its average power.