The site works reasonably responsively – tested on Android (Lollipop, Marshmellow) & Windows 10 (Chrome, Firefox, Edge):
Samsung Galaxy S3
Samsung Note 4
Circa 2009 Core 2 Duo laptop with discrete GPU
Haswell I7 with on-die GPU, portrait and landscape
Sandy Bridge I5 with discrete GPU
https://app.crossbrowsertesting.com for OSX and IOS (Safari)
The menu design I adapted from an existing left-hand-flyout menu is quite space-efficient and for limited items works well on different touch/non-touch devices with different display sizes. The controls-surface sizes are large enough such that the menus shouldn’t close spontaneously too easily from lost hover state while still using hover state for persistence (except for keyboard and touch interaction) so no inconvenient extra clicks required.