Looking for cheap and as light as possible chain guide for my do it all hardtail. Will be used on bumpy peak descents, a bit of dh, some bmx track, will a top only guide be enough from experience?

You can either ‘get away with it’ using a top guide, or be confident and not worry about it with top and bottom. Look for a second hand E13 LG1+ and you can take off the lower guide in seconds if you want to.

an E-13 TRS+ Single would be the best thing for you. It’s basically an LG1 without the taco bashguard. The backplate’s slimmed down quite a bit so it is a fair bit lighter than the LG1. It’s also a fair bit cheaper than the LG1+

I use one on my XC bike (125mm full sus) and it’s great for that, but I also used it on another bike for the Megavalanche this year and it was spot on.
For full on DH I’d want something with a bashguard, but for general purpose stuff I find it’s just overkill.

I have a superstar bb mounted top guide on my Cotic BFE and it hasn’t dropped the chain yet despite some challenging riding. Perfectly happy and confident in it performence

I use an XC only Pauls top mount on one of my play bikes, Ive ridden everything on it and yet to drop a chain.

Perhaps try a seat tube clamping top-only guide Superstar and some others do these I believe, and if you find you have an issue with the chain coming off still, then consider adding a bottom roller, say a Blackspire stinger, that would give you a reasonably reliable and flexible solution, pretty cheap too…