21. SELECTED QUARTERLY CONSOLIDATED FINANCIAL DATA (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	May 31, 2021	Feb. 28, 2021	Nov. 30, 2020	Aug. 31, 2020	May 31, 2020	Feb. 29, 2020	Nov. 30, 2019	Aug. 31, 2019	May 31, 2021	May 31, 2020	May 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 7,638	$ 5,267	$ 1,683	$ 2,012	$ 3,773	$ 6,111	$ 6,874	$ 5,533	$ 16,600	$ 22,291	$ 21,056
Gross profit (loss)	3,534	1,894	377	227	(93)	2,991	3,202	2,271	6,032	8,371	7,602
Net income (loss)	$ 567	$ (735)	$ (1,966)	$ 107	$ (2,885)	$ 245	$ 251	$ (413)	$ (2,027)	$ (2,802)	$ (5,235)
Net income (loss) per share basic and diluted	$ 0.02	$ (0.03)	$ (0.08)	$ 0	$ (0.13)	$ 0.01	$ 0.01	$ (0.02)	$ (0.09)	$ (0.12)	$ (0.23)