I have only used my chinese diesel heater for 4 nights so far so I can't comment on reliability but as far as cost of operation it is quite cheap.
I bought the 5KW version for $142 + $26 for some stove pipe and fasteners to get it through my relatively thick foam floor.
I also spent maybe $5 on electrical supplies to switch it off completely when not in use due to it using ~.1 amps at all times
All nights I have run it it has been a low in the mid to upper 30s and the camper has warmed up in 15-25 minutes.
I am basing my fuel usage of a .03ml per dose from the pump which is the absolute upper bounds for the pump.
For my 9 hr run with about half an hour being start up including the high output to warm up the camper I calculated about .1 gallons of diesel used and that seems about right.
0.00000528344(gal) per dose x 5.5(hz) x 1860(s)(~30m) = .048 (gal)
0.00000528344(gal) per dose x .8(hz) x 34200(s) (9.5hr) = .144 (gal)
Totaling ~.193 gallons or about $0.77 for a night of heat ($4 a gallon)
This means that you will get about 10 nights of heat give or take in these conditions with the 10L tank.
Do you have electrical consumption for the propex for 10hrs? My diesel uses about 11.4 amp hrs
MR Buddy can be useful for recreation but for camping in the cold I feel its not a good fit. Too much humidity and non vented generally don't make me sleep easy. (they might make me sleep too easy and way too long)
My Comparison of the other two are
Diesel Heater
Pros
Cheap Initial Investment <$200 for chinese kit from amazon+ odds and ends
Cheap running cost (for your 10 hrs I calculate $0.58-$0.77 depending on fuel price ($3-$4) and dosing pump error) probably closer to the $0.43 right now
Fairly easy to install yourself
Very easy to find fuel
Parts aren't hard to find.
Doesn't use much electricity when running (about .95 A or 12W)
Turns out that propex is better with its on off abilityYou stay dry because all the combustion stays outside
I can see how much diesel I have left just by looking at the tank no phone required

Cons
All repairs you will probably have to do yourself (pro for some con for others)
Installation you will probably have to do yourself (pro for some con for others)
Startup and shutdown use a lot of electricity (about 1 Amp HR) (only matters for boondocking)
The dosing pump clicking (you can make it quieter but generally you can hear it click Click CLICK !!CLICK!!!)
Stinky especially on startup and shutdown (combustion outside so not your problem except.....
It doesn't ever shutoff all the way unless you power it off. It will idle down to its lowest setting. This is fine if its cold enough that it has to cycle down and up but if its not then cracking a window will be your only hope to not cooking alive. I open the window on the opposite side of the camper to adjust temperature inside so I don't get the diesel smell inside.
Propex ( I don't own but what I've gathered)
Pros
Fairly quiet
Minimal/no smell even outside
Keeps you dry because all combustion is outside
Uses 1.6 amps of electricity or less all the time so startup and shutdown are less of an issue
Probably safer than the Chinese diesel heaters even though the diesel does have some protective circuits
NO DOSING PUMP CLICKING!! (can you tell that's my least favorite part of my heater?)
Cheap to operate according to Cosmo $0.62 for 10 hrs
Edit: (Cosmo told me some info) Electric Consumption 1.4A while running (I'll use 1.6 which is the max from propex) For comparison my diesel uses 4.4A on high
Cosmo says his runs about 12min/hr so at 1.6A that is around .32 AmpHrs/HR or 3.2Amp Hrs for 10 Hrs Compared to 11.4Amp/Hrs for the diesel.
Cons
High Initial Investment
You should probably have professionally installed due to propane however I would probably do it myself.
Propane can be a little harder to get than diesel.
EDIT Moved Electric Consumption to Pros after talking to cosmoReplacement Parts/Service??? Overseas company
I probably would have opted for the Propex if it wasn't so expensive. If you're on the fence I would say go Propex. Its quiet and isn't smelly and may keep you more comfortable with its ability to turn completely off. The diesel may have some advantage in places that don't have propane readily available but you can plan around that with and extra tank of propane.