They seem pretty good for not trapping too much heat, but we have quite cool summers here so what I would consider an unbearably hot day is probably different to most people. I could comfortably sleep in it under 24°C, anything above that and I can’t sleep no matter what type of blanket I have anyway. There are cooling ones made of cotton that might work if you’re in a hotter climate but they cost a fair bit more.
I’ve tried tailscale and cloudflare tunnels in the past and ended up just using PiVPN to set up a WireGuard VPN on my Pi5. Tailscale for some reason was very slow for me, and cloudflare tunnels have a 100mb limit iirc which isn’t ideal for streaming. PiVPN is quite straightforward, it sets everything up for you and all you have to do is forward a UDP port. That was the bit I was most worried about, but, unless I’ve misunderstood something, because a UDP port will just ignore invalid requests to the outside world it will appear closed so it’s not very risky. It then generates a key for each device which you can scan from a QR code onto your VPN client. I have my phone set to auto-connect to the tunnel when I disconnect from my home wifi network and the tunnel is fast enough that I’ve accidentally turned off my phone’s wifi connection before and streamed a TV show through the tunnel over mobile data and not noticed any difference in speed.