I spent a few hours modifying my Gaggia the other evening.
Added the PID temperature controller, pressure gauge, "dimmer mod", power switch and top box:
View attachment 366625
Available at Shades of Coffee:
https://www.shadesofcoffee.co.uk/post-2018/topbox-bundle-pro-evo
When I first looked through the instructions, all 160 pages of them, I wondered if I had made a mistake. However, it's actually fairly straight forward, albeit, fiddly working with the nest of wires in the cramped space within the Gaggia:
View attachment 366627
In any case, once I'd installed all the relevant parts, put it back together and set the parameters on the PID, I switched it on and it all worked, and has continued working for the past 3 days.
Everything seems to work well, but if I were to criticise, the fit and finish of the top box could be better and the instructions could be more concise. While the instructions are comprehensive, they are very wordy. A few wiring diagrams and steps broken into neatly ordered bullet points, rather than long paragraphs, would make the process far simpler to follow. With the addition of a few wiring diagrams, I reckon I could re-write the instructions and get them down from ~160 pages to about 30 or 40.