When I can buy bitcoin directly and hold it, why the need of any third party? Not your key not your coin on the blockchain, no full control.
Some pre-points to consider before doing this, should include an up to date status for security, charges/fees, and the risk of loss(es) in mind.
The fee is always far higher.
For example, a company like Tesla, holds over billion dollars in Bitcoin and is known to have accepted Bitcoin payments in the past. It is one of the top choices amongst a host of others who use and accept crypto currency for payments and trade.
Yes, not accepting bitcoin payment again, but bitcoin remain to be a valuable coin.
Are there any other methods you know, that one can buy/invest in crypto from without using a regular exchange or trader?
Direct peer-to-peer and exchanges are the means to buy bitcoin and it should be sent to a noncustodial wallet (cold storage and hardware wallets are safer) that you have its seed phrase that can always generate the keys and addresses.