Had a bit of time in my hands, so decided to put together a NEC model of the antenna and simulate it, the model is the following
CM -------------------------------------
CM lldoublet.nec : linear loaded doublet
CM -------------------------------------
CE
' design symbols
SY vspc=0.05 ' vertical wire spacing
SY feed=0.10 ' feedpoint spacing
SY hgtA=10 ' upper wire heigth
SY hgtB=(hgtA-vspc) ' middle wire heigth
SY hgtC=(hgtB-vspc) ' lower wire heigth
SY wire=0.00125 ' wire radius
SY leng=18 ' total arm wire length
SY arms=((leng-(feed+(2*vspc)))/3) ' folded arm length
SY freq=7.150 ' test frequency
SY segL=51 ' long wires segments
SY segM=1 ' mid wires segments
SY segS=1 ' short wires segments
' feedpoint unloaded sections
GW 1 segM 0 0 hgtA feed 0 hgtA wire
GW 2 segM 0 0 hgtA -feed 0 hgtA wire
' horizontal arms
GW 10 segL feed 0 hgtA arms 0 hgtA wire
GW 11 segL -feed 0 hgtA -arms 0 hgtA wire
GW 12 segL feed 0 hgtB arms 0 hgtB wire
GW 13 segL -feed 0 hgtB -arms 0 hgtB wire
GW 14 segL feed 0 hgtC arms 0 hgtC wire
GW 15 segL -feed 0 hgtC -arms 0 hgtC wire
' vertical junctions
GW 20 segS arms 0 hgtA arms 0 hgtB wire
GW 21 segS -arms 0 hgtA -arms 0 hgtB wire
GW 22 segS feed 0 hgtB feed 0 hgtC wire
GW 23 segS -feed 0 hgtB -feed 0 hgtC wire
' ground parameters
GE -1
GN 2 0 0 0 13 0.005
' wires loading
LD 5 0 0 0 58000000
' feedpoint
EK
EX 0 1 1 0 1. 0 0
' initial frequency
FR 0 0 0 0 freq 0
' end of model
EN
the antenna uses the original size (see
here) and in the model it's placed at 10m (33ft) above ground, willing to simulate different heights you may just change the "hgtA" symbol in the NEC file; at any rate, the image below shows the antenna vertical and horizontal radiation patterns on the 80, 40, 20, 15, 10 and 6 meters bands
as predicted (assuming my NEC model is correct), on 80m the antenna is NVIS, but things start improving on 40m and, on 20m the radiation angle is good for DX; given that it's cheap and quite easy to build and that it may fit in a relatively small space, I believe it may be worth some consideration; again, it's not a beam or a full size dipole, but if you want to get on air even w/o having room for a full size antenna, that doublet may be ok
Notice that if you can't run the 300Ohm line all the way to the shack ingress, a workaround may be running the line down to about 1ft from ground, connect it to a balun (the original design uses a 1:1, if you want you may experiment with a 2:1 or a 4:1) and from the balun, run a length of coax to the ATU in your shack