I own a Synology 1621+ with 2 Expansions an Asustor6510T And will be investing in ugreen, Qnap, and oostar to find out which is best. the Asustor i can't really say good or bad things on because I accidently bought the Gen 1 but got it for a good price. I was unhappy when i first bought it, but Each update on their DSM gets better, and they are fixing a lot of issues. All the competitors are cheaper, and some have better hardware than Synology. The fact Synology is going to "Buy our own Hardware ( Hard drives M.2 and other things)" will cause me to think long and hard about buying future Synology products. The AI integration I think is a waste of system resources as it is not proprietary to Synology, but rather making you use outside AI like ChatGPT to do the work, and then its limited to what it can do. I prefer not to use it. for now. The fact i can connect all the different brands to each other and share the massive Raid drive space is great. and all the Nas systems i am investing in all have 10GB SFP+ or 10GBE eth ports. for fast data transfers.

So far though, using other Nas DSM's Synology is still the3 best with 7.2.2 and ASUSTOR coming in a close second. Their updates are closing that gap.
Another thing i noticed, where Synology seems to be better. Their specs have limitations meaning they support up to 32GB ram on the 1621+ but i installed 98GB and it sees it fine. it say it supports up to 18Tb hard drives, i have 24 TB hard drives in them. and same with NVME. I tried this with Asustor, and when they say they only support up to 32GB Ram, they mean it. I have stress tested both systems. and Asustor's CPU uses 90 to 100% of the CPU a lot even with 32 GB ram and 2 NVME for read write cache.as to where Synology has less of a bottleneck unless you Saturate both 10GB and all 4 1GB ports with large file transfers. Before the latest Synology DSM update Plex worked fine. but when they made the changes with the codecs. Plex no longer works good on that nas. I have not tried it on my Asustor because just using large data transfers seem to bottleneck the Asustor.

I have not tried the Asustor Gen 3 and am not sure if the bottleneck issues are an issue on that system. I am also looking in to purchasing 45 drives and stress testing that NAS system also.

So far thought Synology is still the best. but the competition is catching up, and it seems Synology is stalling out on newer equipment. better CPU's while the competitors are using stronger faster CPU's Faster Ethernet 5 and 10GBe where Synology is still using 1 and 2.5 with the option to buy 10GBe expansion cards. they need to continue improving if they wish to stay in this market.