sub frame = more power in backhoe without tearing up your 3pt hitch.
for me, seat needs to do a 180 turn and operate backhoe right from the same tractor seat. other wise for me it would be a pain in the rear to get on/off tractor multi times.
some units run off a seperate PTO hyd pump that connects to PTO shaft on back of tractor, while others connect directly into the HYD lines already on the tractor.
there is a good amount of 3rd party backhoes out there, bit it is a mix and match between "sub frame" that fits your tractor, and GPM (gallons per minute) / HYD pressure (1500,2000,2500,3000 ranges) your tractor has and if it needs a PTO hyd pump or not. your max pressure is what going to beef up or not lifting power. and then your hyd cylinders diameters. GPM can be on the slow slide and still be awesome. i don't think i have ever run fully throttle exception a quick jerking of some tree stumps, to try and bust the roots out. but then quickly let the throttle down / RPM's go back down for a slower GPM from the pump.
18" buckets are all fine and dandy, but wish i had an 8 or 10" bucket myself maybe a little smaller for trenches (depends on how wide the backhoe is itself for min size bucket you can use)
i think i have a 20 inch or 30" on the TLB i have, it is just way to big for trenching, it is good to quickly dig the backhoe bucket teeth down, and dig up a big area and pile it up in a couple minutes. and then turn things around and start moving dirt with the FEL. and sizeable bucket to compact ares of dirt. the large bucket good for putting in septic tanks and septic fields (digging them out), but for water lines, gas lines, electrical, telephone, internet, cable tv like lines. 18" is over kill and it just takes up to much.
the "max reach" / max depth can be an issue. longer / deeper the less times you have to re-position the tractor for trenching and like. if your digging a basement, then you should be looking at an industrial size tractor that can easily reach those depths for a basement and have the reach at the same time.
reach for me comes in along the lines of pulling fence posts / putting metal fence posts in. and swinging back and forth from a trailer full of posts or putting old posts on.
how high it can extend up, is moving stuff on/off of a truck bed.
temporary power poles, and light poles (30-40 footers)
temp power pole they don't have to be that high up in the air do they? or that long. but the 30-40 footer light poles, not a clue about that, i think i would rather have a regular "oh forgets the stinking name" combo man lift / hook that varity of tree cutters use and electric company use. that has the extra telescoping arms and reach and height all there.