First of all, almost all snowfoam lances can be adapted to pretty much any machine. So no concerns there :thumb:
For me your post breaks down into three questions which I'll try to answer in turn.
What are the benefits of an ebay special going to be over my plastic jobbie?
The point about eBay is that there are all manner of companies selling pressure washer parts on there, and because they are frequently selling to pros doing Real Work (TM) (eg, cleaning wagons, heavy plant, farm machinery or premises, etc) they are selling gear that's much better quality and more durable than the made-to-a-cost stuff from Homebase or B&Q.
So it provides the possibility to specify your own trigger, lance, extensions, nozzles, etc etc. Plus because all this gear typically uses a standard set of connections, you're no longer restricted to whatever attachments your manufacturer sells. And, if your machine should fail and is not repairable, you can keep the nice gun, lance, nozzles etc and just change the machine (possibly with a new adapter). And because all the parts are interchangeable, you can replace parts that fail or frequently get spare parts and repair it yourself.
You can expect to pay a bit more for it though - for instance, the lance setup I suggested earlier in the thread is £65 - £80, depending on how you specify the connectors, which is the price of a whole budget PW.
So you get better quality, durability and repairability, choice of configuration, but at a greater financial cost (albeit one that you should only really need to spend once).
I am building a new workshop and have the opportunity to permanently install the PW and make up a long hose reel
A new hose, regardless of whether or not you get a reel, is a very worthwhile thing if you have a budget PW. Typically the stock hoses are made of thermoplastic which is liable to tangling and kinking. A "proper" rubber hose with steel wires is much more durable, as well as easier to handle. Replacing the hose with an aftermarket one provides the opportunity to get away from manufacturer specific terminations, since a good hose is an appreciable investment!
My PW came with a 10m hose but I found this wasn't as long as I really wanted, and it was taking a lot of time to get out and put away. As I pretty much always wash my car (or any other car!) on the drive in front of the garage, it made sense to get a longer hose with a reel and mount it on the wall. If you expect to use your PW mostly in the same place, then a reel makes a lot of sense (but if you're going for that option budget for a bit extra hose, you'll likely want it at some point!)
Permanent installation of a PW is also a nice idea, you can have all the power and water ready to go, with the tug of a hose and the flick of a switch you're all ready to go. The same comments apply as for the hose - if you're mostly / always going to use the machine in the one place, go for it. If you might want to take it to a mate's house, or around the back to do the patio, or whatever, then it's worth thinking about how to set it up so it's not too "permanent" :lol:
It's worth noting that some PWs have built in high quality hoses, guns and reels, and come with sturdy wheels (which is just as well since they are very heavy!) For instance, the
K1152 TST. It has the "guts" of a
HD10 but a very robust chassis with wheels, really good quality gun, lance, hose etc. If you look into what this would cost to do separately, well, you come to a number considerably greater than the cost of this machine, especially for the GB price. Plus it's all portable if you need it to be.
All of this brings me neatly to your last question
should I buy the Kraenzle?!
If you can afford one, absolutely. They are superb quality, and while they are not always the absolute best performance for the price, the reason to buy one is the knowledge that in the unlikely event of a fault, you'll be able to get spares, exploded diagrams, etc for years to come.
Again if you can afford it, the K1152 TST is very good value given how much it would cost to get all those things separately. However if you want to do things piecemeal and spread the cost, you could start off with a new hose (probably the best bang for buck upgrade on any budget machine) and then upgrade the gun, add a hose reel, etc, at a later date.
One final point - if you have any ideas of running a Kraenzle off stored water eg collected rainwater, you want to go for a machine with a 1400rpm motor. If you'll be running it off mains water (or you're prepared to install a pump to use rain water) then motor speed doesn't matter
per se.
Edit: Just seen that Elite are offering the
K1050 TST for £420 which is
a stonking bargain as long as you don't need a 1400rpm machine (see above).