Crystal poi + one mass = 95g, 2 mass = 125 g.
Monkey fist weight depends on which one - it'll be listed for each on the HOP page. Remember the chains for fire will weight a lot more than cords.
Each has advantages and disadvantages - fire is brighter, more work, more impact. Flowlights IMO are prettier, and need less care to use safely.
I find both can be seen quite well at dusk, or on heavily overcast days but pretty pointless in Aus in full daylight.
If you keep spinning I'd expect eventually you'll want both led and fire poi, which to go for first is a matter for the individual (I started with led poi, but was spinning by myself)