The synergy plexi is a whole different animal than a Randall plexi because it has two gain knobs per channel and it acts more like a JF or SM mod in some respects, although their mods have more option sonically.
The synergy gives a completely different palette of tones depending on how gain I & II are set. It acts more like a super lead, but I’m not a Marshall expert. The Randall plexi is simpler in that there are only 5 knobs.
Guess the real answer is how hard is it to find the sound in your head and if you like to tinker with knobs or just use your fingers to get your tone. There are more tones to be had with the synergy, if that is what you are after. The Randall is not bad at all either.
Not sure if that helps.