MSA plans are a special type of Advantage plan with special rules.
Medicare participating providers accepting new Medicare patients must accept new MSA patients. Non-participating providers do not have to accept the MSA plan.
The premier cancer centers like Sloan Kettering, MD Anderson, and Mayo Clinic (AZ, FL, MN) have restrictions on some MA HMO/PPO plans but are required to accept MSAs, except for Mayo in AZ and FL which are non-par.
I agree MSAs are rare and policyholders can face pushback from providers that don't take MA HMO/PPO plans. MSAs give members a form letter to show those providers when they are legally obligated to accept the plan.
MSA plans are not like an HMO. There are no provider networks, no referrals, and no pre-authorization requirements just like with original Medicare. MSAs use the same fee schedule amounts as Medicare. Non-par providers accepting MSAs can balance bill up to 115% like Medicare. These 'excess charges' do not count toward the Lasso plan's deductible and are not paid by the plan. MA HMO/PPO members cannot be balanced billed.
The Lasso plan has been available for a year. The $3240 deposit seems artificially high to attract enrollment. A deposit in the $2500 range is probably more sustainable in the long term.
Medigap plan G-HD has a $2340 (2020) deductible that acts more like an out-of-pocket maximum. Medicare still pays 80%. You pay 20% of the low Medicare approved amount until your 20% (and Part B deductible) totals $2340. Then G-HD pays the 20%. The premium is about $50/month. You would need to purchase a separate Part D drug plan with either choice.