JG would be my last choice. Sorry.
Hepworth push fit is the best I've come across to date, and even with its higher price tag I'd still think twice about going for JG SpeedFit. The inserts for JG are very thick walled, especially their 'super seal' ones, whereas Hep ones are slim stainless sleeves which don't infringe on the internal bore diameter anywhere near as much. Quite important when you're designing for 10mm runs to basins / other outlets and you don't want a trade off between delivery losses and flow rates.
The diamond tray I fitted was a one piece jobbie that had the waste outlet offset with a simple / clever design that meant to miss a joist you just rotated the tray by 180 degrees.
It's currently and happily nestling away under those mosaics as we speak. . Been in for 6 - 8 months or more now and zero complaints. I'm in regular contact with my customers so I get real life feedback which is helpful.
That pic shows the 300/500mm offset, and the joists ran parallel with the length of the tray, so an 800mm wide tray with a centre outlet would have landed 3/4 onto the second joist. Impey are the innovators though as they do a rotatable 'double off-settable' outlet which is second to none.
This pic shows ( look carefully ) the MBC pozi joists ( with the metal webs ) and then the ~15 lengths of graded CLS timber ( 3x2 ) that I retrospectively added to provide support for the Impey former shown. Impey say that they're happy with less, my OCD says otherwise ( and CLS is pennies in the grand scheme so I choose belt and Bracey-McBrace ).
The mosaics got grouted with an anthracite grout and looked great alongside the Amtico. Word of warning, the bars in the Amtico ( where the joins are ) want to suck the grout wash-up residue in with capillary action. Mask the edges well as it's a right pita to be cleaning that until 3am, ask me how I know .
Solvent weld waste of any decent make will be fine. Most important discipline is cleaning the swarf / burr from inside the pipe after each cut. Failure to observe that will leave a rough 'crown' inside each joint where hair will snag and cause issues later down the line. From an ongoing self-maintenance POV I always run 50mm waste to any shower / tray / former etc and always make sure the pipework can be got to for rodding later down the line. Always try to avoid 90o bends, and use 2 x 45o bends instead, slightly separated, which will make rodding / clearing much easier and make the run 'further penetrable' during such action.