Many thanks for the comments, which were of a supportive nature. I am sorry for the delay in replying, but I have been laid low with sciatica.
If I go back to about 1978, when I first started brewing, I used to buy ingredients from a local chemist (no Boots in those days). The malt extract was dried, and hops were loosely packed and I cannot remember whether they were just “hops” or Fuggles or Goldings. Looking back, I can see that the extract would have been of a “food” grade rather than a “brewing” grade; and would have been responsible for the homebrew tang that acted as a discouragement to my efforts. That changed when I became aware of Brupaks’ excellent LME. That acted as a spur to my “career”. I suppose that this explanation goes some way to explaining my original question about the quality of alternative LMEs. On that point, I mentioned Brupaks, Muntons and Briess, which are all excellent. I have used Coopers once, but I found it darker than I would have liked, although the flavour was decent enough. I have some Mangrove Jacks for my next brew - the first time that I will have used it. One thing that I ought to have mentioned about the other LMEs is that Beer Hawk offers some more exotic products, such as Munich, Vienna and Rye LMEs. Their options as to weight are of a matching exotic nature - 1.43 kg or 2.72 kg - but I am sure that we could work around that in designing a recipe.
Dealing with the various queries:
1. Styles. My focus is on comparing hops rather than brewing to a specific style, and I use a more-or-less standard formula of 1040 OG and bitterness of around 33 IBU. While all of these are pale ales (so that the malt does not interfere too much with the hops) I do occasionally brew a dark ale, which might be a mild or a porter. (Briess do a porter extract, which is superb).
2. Steeping. Yes, I sometimes steep crystal or carapils grains.
3. Favourite hops. Quite a few years ago, I came upon a description of Cascade as being one for the hopheads, and I decided that I wanted to be a hophead! Thus it was that Cascade was for a long time my favourite, but that changed when I brewed with Mosaic - such a complexity of flavours! I was so influenced by this hop that I brewed with it again within a short time, which is rare for me because I am always anxious to try another hop.
I think that my second favourite is Apollo. I gave a couple of bottles to a member of my tasting/testing panel, who happens to own a pub so should know what he is talking about, and he commented that I could brew that one again!
My next brews will use Equinox/Ekuanot, Enigma, Hull Melon and Eureka (single-hopped).
4. Yeasts. Yes, I quite often split my brews to use different yeasts. I have not yet found any objectionable, but there are differences. They are subtle ones, which are beyond my powers of description! They provide another interest for my tasting/testing panel.
(My reason for trying different yeasts is a little bit of a story, but it explains something about my brewing history and may give a guide to those - shall I say? - of a certain age. I used to follow the advice of, for example, Graham Wheeler, and move my stuff to a secondary fermentation vessel. The time came for me to renew my FVs, so I chose the wide-neck, screw-top variety. My choice was aided by the fact that Tesco were offering them at £10 each. Anyhow, I bought two of those.
A little time after, I read on the internet somewhere that using a second FV is unnecessary for beers such as those that I brew - i.e. not of the knock-out variety - so I decided to use one FV. The results were very good, thus meaning that I had a spare FV of 5 gallons capacity.
More recently, and you may recall that I am now in my 76th year, I have been thinking that lifting 5 gallons of ale is rather strenuous, so I decided to split my brews into less heavy weights. If I was going to split them, why not use different yeasts?)