I think it depends on how severe it is. The one that I tried is using a small bottle solution sold in Giant called Tomcat. I bought it back in 2008 for RM 8 and I'm still using it. I just cleaned my huge panaromic sunroof (aargh) by hand with it when using Autoglym's Glass Polish did not help. No idea what the Tomcat contains but people say it's strong acid. From the smell, I think it's strong ammonia or something.

There's also another product off the shelf called Forma Hero Rain Stain Remover. Not tired it yet.
From my memory, the Meguair's NXT was better than M21. Easier to apply and shines better. Anyway, it was a while back.
You like paste better? Liquid is usually easier to apply. If using DA machine to polish, liquid is easier to apply. With paste, you need to spread it with something like a butter knife to the foam pad of the DA.

Anyway, I've only used M21 once. Not a good experience if I'm not wrong. Hard to buff off if I recall. And to my untrained eyes, other products gave better shine. Perhaps for durability, it's quite good? I'll try it again and find some time to use it.

Anyway throughout the years, kept buying other stuff and found it better like Meguiars' M16 paste wax. I started collecting other paste wax like 3M Perfect It and Meguiars Ultimate Paste Wax. I like the Meguiars Ultimate Paste Wax. Easy to apply and buff off like liquid and looked very good on black cars. But cannot remember off hand how durable it was. I also bought liquid type wax like M26 Hi-Tech Yellow Wax and Meguiars Gold Class Carnauba Wax which I quite like but does not last long.

The lately hand itchy and got Autoglym's HD Wax when I was in Singapore. Tried it and thought the paste wax was difficult to apply and more picky on surface. Surface must be clean and you need to apply really thin. For a large bonnet and if you don't apply evenly on a dark coloured car, it can get patchy and buffing it to make it same is damn difficult. But in my limited use, durability so far is excellent. Water beads very nicely too after a few weeks.

Yea.. bought

1)Brilliant Shine Detailer
2)AIO Easy Shine
3)Interior Cleaner
4) Wash Sponge
5) Dirt Eraser
6) Cockpit Spray

with some FOC gift as well..
1)MF cloth
2)Plastic Care pad
3) some sample of Windscreen wash 1:100

total is less than RM200..

If i buy with Maguairs i guess the price is more than that...   

i really like the boss there.. he willing spent time with u sharing abt detailing... gd service! 

My DA? Just a humble BD KP600 modified to take normal velcro foam pads and the Bosch GEX-125.

No lah. Just like TT for any car clubs, the people in attendance will talk about anything to do with detailing plus a little bit more. Talk about latest detailing gears and products, where to get what, tips and anything you want to talk about. But basically it's a more social type gathering just to get to know and share knowledge.

I believe this TT practice originated back from Autoworld forum actually when detailing sifus would congregate mostly on Friday evenings at the Banana Leaf Restaurant in Center Point, Bandar Utama.
Not me lah. Instead of using glue, I use a double sided automative velcro tape and line them like it's shown on the link. Easier and faster.