if you just want the popular stuff they will be fine since they keep that since many download it but if you veer off that path they have poor completion since their system does not keep everything. but even then with other services at similar prices you can get better for the same price.
blocks could be a bit restrictive unless you reliably download the same each month so you have predictable usage. if you ever deviate or find yourself having to hold back so you dont burn up your block, an unlimited account may be better and then you dont have to worry. unlimited is cheap enough now.
newsdemon is sadly just not that good with their selective retention when better alternatives are there at a similar price.
i think most others covered it but for provider Frugal usenet is probably best bang for your buck as you get access to two separate systems.
Frugal Usenet is on the same backbone as Usenet.Farm
the unlimited frugal servers are newshosting / omicron backbone. frugals bonus server is what is usenetfarm so both backbones together when you subscribe. shouldnt be any real need for a usenetexpress block account since you would have the usenetfarm backup already but i guess if you find a great sale you could throw it into your newsreader.
i think the only real spot for a curated list of bf deals will be the usenet subreddit. otherwise the shitty affiliate sites wont really show you all the actual deals, just their pay per sign up links.
astraweb hasnt been their own thing for years. they sell the same thing (omicron backbone access) others sell for cheaper.
i dont think any service is going to give you free weeks or a month with no strings attached. if they did everybody would use them and not pay. you can just buy 1 unlimited month of frugal usenet for 5 bucks (not a subscription) and call it good.
Usenet is considered decentralized, it is made up of many independent servers that talk to each other. take one down, and the rest continue on without problems.