The first two links R965 and R8250 are both basic set controllers. The R8250 is actually a worse controller than the R7229 previously discussed. The R7229 is the replacement controller for the R8250.
The R965 is the predecessor for both the R8250 and the R7229. The R965 comes in two variants. The earlier Margate [Made in England] one and the later Made in China one. The Chinese one is the best of the bunch that have been mentioned so far but it is still a relatively low powered DC Analogue controller.
As far as cheap controllers are concerned and for something to use to just check out what you have got before investing too heavily then the H&M Clipper in the third link is a good choice. Many on here rate it reasonably highly. Personally I find the technology inside it very dated.
I shouldn't be saying this as this is a Hornby forum but for a new product purchase of a high power controller rather than second-hand. Many on here use Gaugemaster and/or Morley controllers.
And just so I've understood, on some models you have the controller then a separate transformer i.e. the bit that goes from the mains with a plug that connects to the controller?
The basic controllers like the R965, R8250 & R7229 use a 'Wall Wart' type PSU. 'Wall Wart' means a PSU that has the mains plug built integrally into it. The output of the 'Wall Wart' PSU for the R8250 & R7229 controllers is 19 volts DC at 0.5 amps. The output of the 'Wall Wart' PSU for the R965 is 16 volts AC at 0.8 Amps.
The more serious controllers such as the HM2000 from Hornby have a direct 'mains' input with an internal multi-winding transformer to support multiple outputs. One transformer winding per output. The Hornby HM2000 has two controlled track outputs rated at 0.55 Amp each, plus one fixed 16 volt AC output plus one fixed 12 volt DC output. These two AUX outputs share 0.3 Amps. However, although the HM2000 is the top of the DC Analogue range from Hornby, its 0.55 Amp max rated controlled outputs are adequate but nothing special. Note that there are at least three different variants of the HM2000, and each one might have slightly different power specs to the specs I have stated.
I can't comment on Morley, but the Gaugemaster controllers have models with 'Wall Wart' PSUs as well as controllers with 'mains' input. The GM controller models tend to have outputs of at least 1 Amp as default.
In principle and just purely as a 'rule of thumb' the higher powered controllers tend to have direct 'mains' inputs.
The H&M Clipper will be a direct 'mains' input controller, therefore given its vintage age, caution should given to ensuring that it is a safe purchase.