I've tried to be really clear on that point.
I understand that you're in the UK so I don't know what kind of prices you're looking at. You're asking about spending $99 for a test app and another $60 on a useless "cleaning" app. Although TTP is good, I service a lot of Macs and can justify the cost.
Let's take a look at what things cost: $159 is around £125.
You can get a 1T SSD for £59. It's a Micron 1100
https://www.amazon.co.uk/Docooler-I...e=UTF8&qid=1540948180&sr=8-19&keywords=1T+SSD
An 1100 is the same SSD as a Crucial MX300 (same company) but there's no warranty. It's an OEM and the VARS who use it in their products are expected to handle any customer service issue without sending it back to Micron/Crucial.
Don't buy an MX300 for £179 because there's better value. The MX500 has a 5 year warranty and costs £137, for example
https://www.amazon.co.uk/Crucial-MX...540948806&sr=8-25-spons&keywords=1T+SSD&psc=1
There are less expensive 1T SSDs like the Mushkin but I don't know what the warranty is. My recommendation for you is to go with the 1100. I have never had one go bad but I would get a commitment from the seller on some kind of return privilege in case of a defect.
Do you need the £9 bracket? Not really but it's highly recommended. You can attach it to the foil on the back with double-stick foam tape and people do. I don't.
https://www.amazon.co.uk/Sabrent-De...sr=8-5&keywords=2.5+to+3.5+hard+drive+adapter
The temp sensor on a 2011 iMac. The OWC is the ideal solution and looks like this. The included tape and pick are for the 2012–on but on AmazonUK, it's more expensive without them, oddly enough.
https://www.amazon.co.uk/OWC-OWCDID...ords=owc+in-line+digital+thermal+sensor+cable
Without the sensor, you have to control the fans manually. There are freeware apps that pop up a control panel. I tried that for awhile and hated it.
I know an inexpensive workaround for the 2009–2010 but not the 2011.