I've never head of Lyndall, but their stuff seems pretty good. Like many aftermarket sites they have limited-selection drop-down menus and don't really provide many specs, so it might be a challenge finding something that without-a-doubt fits the SR.
For your front brake... having had good results with it on my bike, I'd highly recommend replacing just the master cylinder.
Some numbers for the '15-'17 SR OEM front brake hydraulics:
Caliper piston area: @ 1509 mm2 (total)
MC piston area: @ 126 mm2
Hydraulic-advantage ratio: 11.9:1
A 9.5mm-piston MC - like the Nissin 3/8 I put on my 'MX' bike - would give the SR a 21.1:1 ratio, or @ 78% more pad pressure than the OEM 12.7mm MC. Any Brembo, Nissin, etc. 9.5mm / .375" MC w/switch should drop right in and make a huge difference, and you won't have to touch anything else.
On the rear, the 11mm MC from the FX (Zero p/n 25-06731) has 49mm M6 bolt spacing / rear reservoir hose / top output / clevis, and should give @ 19% more pad pressure than the SR 12mm MC. This won't be a night-and-day difference like the front MC change, but it should still be very noticeable.