I found Ultra Magnus to have a much more intuitive transformation sequence than Thundertron, if a somewhat uglier alt-mode. The toy manages to make you think but is certainly doable without the instruction manual, which is the kind I like in my Transformers (too easy = boring, too hard and/or fiddly = not worth the time).
I like my Ultra Magnus toys to be some form of car carrier such as G1 and RID (a much undersold figure in my opinion), but having him as something more than a recoloured Optimus Trailer Cab is at least acceptable. It's a blockly and ungainly flat-bed truck with a bunged on armament on the back, but it's ok.
He has his token stems coming out from the tops of his shoulders, though they are very tiny and spiky. He comes with a missile that can be attached in various places, personally I put it in his shoulder aka G1, and it would have been nice if he came with a second one to complete the effect.
His hammer, while being a nice callback to Animated Ultra Magnus, looks stupid in gun mode - frankly I hate pretty much all the guns in TFP and DOTM that look like big lumps unless unfolded. Unless you want to bluetack them in place and run the little battery down, it takes away from the quality of them on display in my opinion.
Worth getting? Well, he's not a very big Voyager (remember when they used to be huge?) but if you can get him cheap (3 pack from BBTS with Thundertron & Skyquake) then he's worth a few bucks. Certainly worth getting over the Prime Beast Hunters Magnus, who may look slightly better in robot mode looks balls in vehicle mode, as a light blue version of TFP Prime.