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I have a cheap one and a good one (looks identical to that but I think I get it from Leyland). Good one is better in use, and the auto-release of pressure to avoid sealant oozing out when you put it down is good. BUT the plunger gets stuck in the moving bit of CT1 cartridges, fucking ballache to get out. It just needs to be 3mm larger in diameter.
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That does depend on the viscosity of the material you have in the tube. Sometimes leaving the tube in hot water for a while or on top of a radiator can help. Some materials do need a more robust frame though.
I use a smoothing agent with my finger to finish bathroom sealants. This bottle has lasted over 10 years and a lot of showers/baths.
Definitely get profiling tools. But I wouldn't get a really cheap gun. They bend and break.
I'm happy with this screwfix on which is still inexpensive, but much more robust than my first.
https://www.screwfix.com/p/no-nonsense-heavy-duty-sealant-applicator-gun/136fr