Questions on Astro-modified DSLR

I'm looking to pick up an astro modified DSLR, I understand there are different mods, but not too sure what the difference really is between them? Another main question, is if I get an astro modified DSLR, is it an absolute 'must' that I use a certain type of filter with it? Or can I just use the DSLR and lens the same you would with a generic stock camera?

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Any advice, or suggestions for videos to watch on this would be great as it's quite a bit for me to spend, just want to get it right and understand before I buy :)