Both HLG 350R and HLG 650R and powered by HLG's latest Diablo Quantum Boards® and offer the same full spectrum. Both are ETL listed commercial Horticulture fixtures and have enough power to replace a 1000W Double Ended HPS with only half the power consumption.
Two HLG 350R may be better for you if you are looking for better light spread, more output and do not mind wiring 2 AC power plugs.
For Veg spaces Two HLG 350R's give you a lot more flexibility on light spread. HLG 650R is limited to only a square footprint.