Oh, yeah, she's a thing of beauty all right. (I have slightly more affection for the DroST-IIa because of some things in its fluff, but enumerating those can wait for a DroST thread.) If you need trash hauled before the advent of modern trash-haulers, or when you're hard-up for cash? Accept. No. Substitutes.
The beautiful part is, the thing's so ubiquitous. Need to make repairs? Everybody builds/built them, so parts will be everywhere, available, and probably cheap. Need crews? Any tramp-sailor who hasn't done at least one trip on a Jumbo is probably too green to be worth hiring. Need to carry (read: smuggle) something valuable without attracting undue attention? Nobody looks past all those dings and the battered paint-job - it's damned near anonymous.
And if you're a sneaky sonofabitch like me, merchant-conversions are still going to be so anonymous, few people will ping 'em until it's too late. Keep the external mods to a minimum, and nobody will look twice - hell, they might not anyway, given the myriad pedigrees and design-architectures you're likely to see out on the space-lanes. (Remember, the term "Jumbo" is applied to more of a design-group than a single set of invariable blueprints; every 'Shipwright will have their own variation on the recipe.) Need to haul a military ground-unit on the QT, like maybe pulling a Trojan Horse gambit on a spaceport? Turn a Jumbo's cargo bay(s) into vehicle-decks or 'Mech-hangars. Want a Q-Ship/"merchant-carrier" for JumpShip escort or to support your ground-troops? Open her up and turn her into a fighter-carrier - you can cram in a full wing of eighteen ASFs into just one hold, and you'll still have the cargo-capacity of the other two for supplies or other uses. (Don't bet against there being a lot of pirate-bands who have their own take on those set-ups. If you do, I'll strip you of every cent you have.) My money says that if you can think of a mod for a Jumbo, it's been done in-universe half a dozen times minimum.
TL;DR: I love this 'Ship. She's an antique beat-up tramp-freighter hunk'a'junk, and God bless her for it. {>{>