Let's consider the climate investments.
tree planting schemes
Do they pay an external landowner to plant trees, or do they purchase the land, plant trees and ensure the trees will stay there?
If they don't own the land, this has exactly 0% effectiveness. Chances are the landowner just chopped the trees down and would in any case plant the trees to maximize profits from future forest growth. In this case, the climate help is exactly zero.
Also, consider this: if you plant a tree, it will grow and be a carbon sink for the next 100 years (in Finland; maybe the growth period is shorter in warmer countries), but after that the forest will be in equilibrium, and no longer actively sinks any carbon. The best choice of action would be to chop down the trees when the forest has grown very old, to get lots of sawlogs and little pulpwood, and replant a forest. Those sawlogs will be used to create furniture, houses, etc. that maintains the stored carbon for 100+ years, and also you get room for a second round of carbon capture by planting the trees again.
In southern Finland, prime forest land costs 7000-8000 euros per hectare. One hectare grows maybe 7 cubic meters per year per hectare, removing 7 tonnes of CO2 from atmosphere per year per hectare. However, a lot of the value of land is the trees on it, so buying something to reforest could be cheaper. If you pay much less than this, most likely they are not buying the land but rather paying some other landowner to plant trees, in which case it's a scam -- the landowner most likely would have planted the trees anyway.
Solar panels are helpful only in two distinct cases:
- The solar panels are installed in an electricity grid where air conditioning dominates electricity consumption. It then correlates really well with consumption, since during cloudy weather less AC is needed and during hot sunny weather more AC is needed
- The solar panels are installed in a climate wíthout true winter, and are installed along with storage batteries that allow using electricity even during times when the sun doesn't shine. Most of Europe for example doesn't fit this criteria, but maybe the sourthernmost parts of Italy, Greece and Spain could be acceptable for year-round solar power production. In Germany or Finland or UK for example, solar power only offers a very little bit of help in summer, in winter it doesn't help at all.
Because of the issue I explained in (2), my primary advice would be to invest in wind power and not in solar power.
I understand that in some parts of the world, cookstoves burn wood and create quite a bit of deforestation, CO2 emissions via deforestation and particulate matter pollution. A better energy source for cookstoves could help, but in my opinion the best approach would be electrification. "Clean" burning of wood still can cause deforestation and CO2 emissions although it could eliminate particulate matter pollution.
Something to consider. In EU ETS emission trading scheme, one tonne of CO2 has a cost of 80 euros. So presumably if you are paying less than 80 euros per tonne, it could be a scam. If you are paying orders of magnitude more than 80 euros per tonne, it could be a scam too -- they charge you too much, pocket some of the money and use only some of the money to offset emissions.