My two cents follow...
I started my journey on the 5x4 with the Yankee tank, mainly because at the time I hadn't read about all its bad reviews. Everything was fine and I liked it except for the need to pour 1.65 l of chemicals for each bath. This was only a problem for me because I did not have 12 sheets to put inside and it seemed a bit too much for just 4 sheets. After spending some time on the LFF I started reading a lot of "violent" critics towards this tank and all the rave about several other systems. I started buying other systems, essentially hoping for lower chemical use. Namely, I bought the Patterson Orbital and the Nikor and tried also the standard trays. After having tried all I came back to the Yankee tank which I have been using in a quite intense way. This is not to say that it is a superior option. I am just saying that for me it is. Thus, don't discard any option based on what you read, specially bashing messages.
Regarding your specific questions...
I don't have a Mod54 but would say the quality of the Yankee tank is good. After having used it well over 100 times it still looks and behaves as new.
As for loading, the Yankee tank brings a slider that guides the sheets. It helped me a lot in the first times, but now I can do it well without any help. I find it very, very, very easy to load . Easier than the Jobo 2509n (I use those for color).
As for the agitation with the Yankee tank. I do it using two main techniques. The first is to wave it sideways like a tray, but I use low amplitude movements never raising the tank more than is required to keep two points of the base on the table (the corner and the base bezel). I also take the lid off and execute vertical movements by raising and lowering, slowly. Contrary to other's experience, I never have problems with spilling.
I guess the most compelling reasons to choose the Yankee are the low, why not say right, price and, even development for stand and semi-stand routines (I know this last one will make a lot of Yankee bashers unhappy ).
I would love to find a version of the Yankee much narrower, for just 1 or 2 sheets. It would be ideal for semi-stand and dedicated development (ZS & BTZS).