Honestly, building your own isn't difficult at all. It's glorified lego for adults. I would highly recommend giving it a go.
However, I can appreciate not being comfortable building. It's not for everyone.
With that, I would suggest staying away from CyberPower, iBuyPower and the like. Their prices
sound good, but once you get into the nitty gritty, they cut corners on motherboards, PSUs etc or really underwhelming coolers.
You don't have any control over those components and, while they should certainly "work" initially, they may not be adequate for long term use in all situations, nor truly fit for purpose.
That specific system doesn't look too bad at all. I'd be budgeting for a better quality PSU and a better CPU cooler if you want to overclock. You might luck out and the PSU it ships with could be 'good'.... but I wouldn't hold my breath. The CPU cooler is a basic 120mm AIO... which is far from ideal for a 9900K.
Depending on what you're looking to spend, this one actually looks like a pretty good deal (relatively speaking) too:
https://www.cyberpowerpc.com/system/Ready-To-Ship-GAMER-SUPREME-ET9917
PRetty much the same setup, but you get a 2080 Super opposed to a 2070Super. Retail-wise there's about a $200 to maybe $250 price delta... Yet they're charging roughly $130. Of course there are other tweaks here & there too, but very very similar overall.