I don't think it's a good idea to use or recommend online QR code generators. You don't have any guarantee that they won't start changing your addresses to one of their own.

Actually, your first QR website (4) is already a confirmed scam: [Warning] Bitcoin QR code maker

Also, Bitaccelerate.com isn't really an accelerator. All they do is push your transaction to the mempool, which doesn't help with getting your transaction included faster in a block. On the other side, ViaBTC's and Antpool's accelerators actually work.

You didn't reserve enough space for the tools. I think there are loads of tools out there that could cover more than 3 posts based on your posting format. Here are a few random ones I came accross minus even looking hard
1. bitcoindata.science by our very own Bitmover. The tool includes a bitcoin units converter, Bitcoin Address Balance Checker and a Plot of your Transaction in the Mempool
2. https://livebitcoindata.com
3. https://iancoleman.io -
4. https://bitnodes.io/nodes/live-map

I like the transactions visualizations, you can see the transactions in real-time with some nice animations, some good examples of these services are:

http://www.bitlisten.com/
http://bitcoinglobe.com/
https://blocks.wizb.it/
https://privacypros.io/tools/bitbonkers/

Feels kind of relaxing to see all that money flow in real-time 

There's a lot of stuff that I do not know here. That must mean I'm no Bitcoin maximalist hehe.
Topic added to my Watchlist anyway.

Do you know of any reliable site that monitors hashrate and mining difficulty only? I was looking for something that is light or easy to load.

Do you often use gobitcoin.io? How often does it go down?
Preev.com is a good converter too but it goes down sometimes.

too many versions of Shamir secret sharing, we must be careful instead of using it. you can recovery by part using a specific source only, for example: if you splitting seed using Iancoleman, you can recover using Iancoleman only. or if splitting using Trezor one you can recovery using Trezor only.

I've even seen also other tools using the scheme with the different sharing, I assume recovery available for that tool only. I just worry if the tool isn't working in the future, the user will be confused to recover his split seed.

# 16 Bitcoin Tools:    Realtime data:Block Eta, Block Probability,  etc.; Hash tools: Pubkey To Address, Address To Pubkey, Address To Hash, etc.; Address lookups: Find Address Sent, Find Address First Seen, etc; and a lot more.

AND

#17 Bitcoin IDE: OP_codes editor, Script, Assembly, Stack Visualizer

have been added.

Don't forget the most import converter you need when you start with Bitcoin. A Bitcoin units converter One like this one https://bitcoindata.science/bitcoin-units-converter.html I still use from time to time. Getting familiar with the Bitcoin units and the abbreviation could be a hassle at the beginning.

I would also recommend and list ycharts.com [1] which shows a ton of good Bitcoin indicators which other similar sites don't. Besides well-known indicators like average bock size, average confirmation time, average difficulty and so on, it also shows data like average transaction fee, average miner revenue per day etc. I check the site regularly to get an overview of what the Bitcoin network looks like right now and where it's headed.

[1] https://ycharts.com/indicators/reports/bitcoin_statistics