Not guilt. Not sin. Your logic is specious parroted re-hash from George Monbiot's failed thought leadership from the mid-2000's. Carbon dioxide is pollution and waste just like household garbage, recycling, and compost. When you offset you're cleaning up after yourself.
As with more tangible-seeming waste, it's always better to avoid and reduce before paying another party to deal with it. Yet CO2 is demonized because global warming is a collective externality. Because it's invisible doesn't make it intangible. Because the reductions can be counteracted by an entity that's in another location doesn't make a difference, either!
Beware b2b with large corporates, especially those that have already professed leadership and concern on climate change. Google, Disney, Microsoft, Apple, UPS, and... Interface. They will wear you out. Maybe they'll have a soft spot for your YCombinator gloss, but don't count on it. Most companies you would pursue are already partnered up w/Natural Capital Partners, NativeEnergy, Carbonfund, etc. It's very rare for them to switch. That gold rush happened long ago. There are of course exceptions and other pockets of opportunity. Don't think you're different, special, better... that "it's different this time" or that hey offsetting is a neat space where buyers can granularly allocate their buys across many different providers. Theoretically true, doesn't happen. Save your energy for companies with newly-announced neutrality commitments. Even then, in our experience, those dialogues move slowly (2+ years), usually involve RFI's and RFP's, and then you're up against 20+ incumbents who have been doing this for over a decade.
They're a 501(c)3 private foundation, similar to a 501(c)3 public charity like COTAP. This makes offsetting contributions tax-deductible. The point is by making it tax-deductible, along with other things like helping folks offset monthly, they've already tried to make it as compelling and easy as possible to offset, but no dice relative to time/effort/$ put in. Similar to StandforTrees.org. I'm basically saying I don't think Wren is different enough, other than charging higher margins, something not in their favor. It is good they're transparent about margins, but that's not unique either.
COTAP here... Thanks to thisjustinm for getting us into the conversation : )
Not to rain on the parade here, just a cautionary tale that is intended to be helpful...
I would say take a look at Cool Effect which launched in early 2016. Charity at a glance, but it's also a bottomless-pocketed family from Marin. It cuts itself checks from the Overlook Intl Foundation, run by the same people. Both orgs have same CEO. All fine...
But look at the 990s... They have thrown the kitchen sink at this and have probably dumped $10+ million by now. $800K+ in PR and marketing before they even launched.
Yet they've only sold well under 1 million tonnes over 3 years. In other words, back of the envelope they've lost $9 per tonne, even when being a charitable donation.
Also, divide their 838,715 cumulative tonnes noted on their home page by their 533,115 cumulative members. 1.57 tonnes/member over 3 years, or a half tonne per member per year. Not anywhere close to the average US footprint.
Half the country doesn't believe in climate change, or it's not a priority, or is living paycheck to paycheck, or all of the above. Offsetting is not anywhere on the horizon of their hierarchy of needs. Offsetting is complex, misunderstood, and controversial (see our op-ed's n TheHill.com for a taste).
When you finally get beyond those nesting subsets, there's enough market size to go around in theory but it's extremely competitive.
As with more tangible-seeming waste, it's always better to avoid and reduce before paying another party to deal with it. Yet CO2 is demonized because global warming is a collective externality. Because it's invisible doesn't make it intangible. Because the reductions can be counteracted by an entity that's in another location doesn't make a difference, either!