Here's something else to think about.
That fire escape, being metal, is going to affect any antenna 'near' it. That 'near' is relative, and not necessarily 'bad'. For one thing, it's going to make any antenna sort of directional, at least in some directions, usually less signal from the 'side' the fire escape is on. Sort of a 'reflector'.
That mass of metal is also going to act as a "ground" to some extent. Which isn't necessarily 'bad' at all. If you can use that characteristic in a beneficial manner, do so, why not!? The 'flip-side' to that is that mass of metal then becomes part of the antenna, will radiate, and means you've got an antenna -that- close to other people's electronics. (See where that could be a problem in an apartment building?)
As antennas go, the best producer of a radiated signal has both resonance and impedance matching. The less of either of those characteristics means less efficiency and radiated signal. Then there are antennas used on multiple bands. They always will be less 'efficient', but will certainly work. How well they work just depends on what you are willing to 'give up' on those non-resonant bands. (I've found that I can give up quite a bit of that 'best' stuff and still have a very usable antenna.)
With the 'end fed' antenna that you have, and from reading it's advertisement, I figure the manufacturer is using the feed line as the 'other half' of that antenna, the counterpoise, 'ground', whatever you want to call it. While that can certainly be done, it always has complications of one sort or another. One of those complications is that the usable SWR bandwidth of that antenna is going to be fairly narrow. Another is that the positioning of that feed line is going to get sort of 'picky'. There are so many variations to that, that there are probably several 'ways' of going about it, and I'm not about to make any recommendations as to how to go about it! Play with it and see?
And here are some observations about the manufacturer's line of antennas. All of them are only variations of things that other manufacturers have had for years. Some of them are only 'good' for very particular situations! Some, you couldn't pay me to use because of experience with them! You will notice that there are no performance specifications given, they leave that to your imagination. (The ones copied from 'B&W' are perfect examples. Don't just put those down, go wash your hands!)
Being one of those naturally 'cheap' people, I don't like buying antennas, I'd rather make them. That means that I very seldom ever have the 'best' antennas, but they 'work' well enough (for me?). One suggestion would be to use that @#$ fire escape as the "groundplane" (hate that word), and a 1/4 wave as the radiating thingy. That's fairly easy for the higher HF bands, and not impossible for the lower ones. I think you might be surprised at the results.
Good luck with it.
- 'Doc
All of the above is a 'generalization'. That means that there are a number of variations possible with any of it, and never always 'correct' as stated.