My philosophy is push to buy the best quality for the money.
In certain instances, buying the more expensive option is justified when you look at the benefits of the item, plus the amount of time you'll get usage from it.
Also, because of the price, it'll have a residual some time down the line if you need or decide to sell it.
In this case, you're buying possibly the best monopod type you can — large diameter carbon fibre. Even if after a year or two you realise it's not being used all that much, you will get a greater percentage back of the price you paid, than if you bought a £30-40 one, which you may be lucky to find a buyer at all, not to mention the better quality and sturdiness, inherent in the design.
If you don't sell it, then in 3-5 years of usage (regular or otherwise) you'll have long since forgotten the cost, and still benefiting from the design specs, whereas after a year or so of using a cheaper, thinner type, you'll maybe realise its shortcomings, and want to consider the beefier option.
That's not to say you won't get away with spending less on a thinner carbon fibre one, but at least with the big one, you are practically guaranteed it being a one off purchase, with a 5-year warranty.