Being one of the lucky few to get my Steam Frame a few weeks ago, I have been using it quite a bit since then. I have been buying some third-party accessories to mitigate some of its weaknesses.
First the obvious one: it is surprisingly light and small, but overall not comfortable enough due to my glasses. To solve that I went ahead and bought prescription lenses from VR Optician (119€ including fast shipping and additional prescription fee).
Then I figured I had better protect it against sunlight because I do not have one of those fancy head mounts nor do I want to pack it in its box between each use. Thus I got an AMVR lens cover that fits quite well (13€).
And finally the battery life situation is... Well it's bad. I got decent VR legs and can play for hours, but the battery only lasts at most 1h30 when running PCVR at 120Hz. So I got myself a UGREEN Nexode 145W 25000mAh Power Bank (56€), 2 short angled USB-C cables (24€), round magnetic USB-C adapters (16€) and a small fanny pack (10€).
I will also say there has been some trial and error regarding the magnetic adapter. The idea is to protect the headset port in case the cable snags on anything. I wanted to plug it directly in the headset port, but it tends to disconnect when I turn my head. The tradeoff I landed on is : one very short cable plugged in, magnetically coupled with a longer one that goes to the battery. The 240W-rated USB-C cables are also overkill but hey, not that much of a price difference (they are quite thick though and contributed some in my disconnect issue).
So there you have it, 238€ on top of the initial Steam Frame + ergonomic accessories kit purchase (which is a must-have if you ask me), not counting said trial and error.
Update: there are strong arguments in comments against using magnetic adapters. I'll be ditching that and keeping the 2 cables approach so that there is a straight connection (hopefully weaker than the angled plugs) that can unplug more easily than the battery or headset side if the cable snags on something.
Well shit, I had not thought of that. So basically it's a choice between risking damaging the connector with physical movement or damaging the electronics inside with conductive dust. I do not expect there is much metal dust floating around in my home but I'll keep that in mind.
The entire head strap is technically replaceable, but the USB PD power circuit, as far as I know, is in the core module, not the headstrap battery thing. (When charging, the power goes first to the HMD itself, then loops back to the battery. This makes sense, as it would have to be this way for any future headstraps that run wired with no battery to be possible.)
So if you fry it, you'd be replacing/repairing the core module, not the head strap.
So I'm risking the port.
Alright you have convinced me. I'm ditching the magnet connectors and taking my chances with regular angled cables.
What I did with my old quest was to plug the cable into the headset, leave a little loop of slack in a way that doesn't get in the way and secure the cable itself to the headset strap. So if anything yanks on the cable it'll yank on the headset strap and the slack loop will keep it from torquing the port. I used velcro cable ties and it worked pretty well. Make sure the cable is long enough to have slack at the battery end too to account for movement. I'd usually run the cable down my shirt and it did just fine.
I did something close with my Quest 3S when using it seated: angled usb-c connector into the port and cable velcro'd to the strap. However the placement of the port is very different on the Frame so I cannot figure out how to reliably (and comfortably) secure the cable to headset. Hence my experiments with magnet connectors.