I've owned many Givi top cases and side cases, including OEM ones. I've also crashed one and it held up better than the bike did. I'd recommend never paying list price for one. There are often significant discounts if you are patient and check multiple retailers, and you can sometimes get a screaming deal on them used (CL, FB Marketplace, ADV Rider) since many people buying Givi don't want to buy one with some scuffs or scratches on it. Some Givi models can also be found cheaper under the Kappa brand label which is their more budget friendly subsidiary, but I don't think there's a Kappa version of the DLM30.
One of the best selling points is when Givi offer a lock cylinder that can be rekeyed to your bike's ignition key, so that you don't need another key. Beyond that, they have good support but you'll have to pay for replacement parts like gaskets when they go. On an off-brand one, you may not be able to find a replacement gasket, but DIY is an option for things like that, or for the cost you may just be able to replace the entire thing and still be out less money than if you had paid list price for a Givi. But like Perazzimx14 mentions, it's a storage box. You want it to lock and seal, so if there's an off-brand one that looks suitable for much less, I wouldn't steer away from it. If you pick one up, I highly recommend adding a stretch net to the inside of the lid. It's very useful! I also carry some RokStraps and a cargo net for adding items on top of cases like that.
