Is there a reason not to use it?
For the summits in DM carrying additional 100 g normally is not a problem. So I do not see the need to use RG-174. When using a 5 mm cable, why stick to the old RG 58 when Aircell 5 or Hyperflex 5 are available? Attenuation normally is not a problem with a few meters of RG 58, but I cannot see any advantage of RG 58.
I have been using 5 m of RG 58 for my HF activations for many years. For VHF/UHF I switched over to 5 m of Aircell 5 (Hyperflex 5 was not available at this time). As I use the same cable for HF and VHF activities now this is my standard cable for HF, too. I have used it many years and propably more than 200 activations. No problems with the foam dielectric due to mechanical stress up to now.
The big advantage of an EFHW: You can reduce coax cable length as you can sit near the feeding point of the antenna.
Generally this works fine, as discussed in Should I use my vertical horizontal? More results - #5 by DB7MM
But especially on DM/BM-344 this is a bad idea: All the telecom equipment installed in the lookout tower causes QRM when your antenna is near to all the cables running down down to the ground.
So for my last HF activation I set up at the bench a few meters beside the lookout tower. With a EFHW and a pole this should work fine.
73 de Michael, DB7MM