MBB vs MTBA

MBBAiShares MBS ETF

MTBABSimplify MBS ETF

In short

MBB Launched in 2007, MBB is the plain-vanilla way to own U.S. agency mortgage bonds: one of the biggest and busiest funds in a small niche, tracking the Bloomberg U.S. MBS Index for four basis points.

MTBA Most funds in the aggregate-bond aisle buy a little of everything. Simplify's mortgage ETF goes one lane deep: agency mortgage bonds, actively run, launched in 2023, paying monthly.

Stated mandate

MBB The fund seeks to track an index composed of U.S. agency mortgage-backed securities.

MTBA The fund seeks total return while preserving capital through prudent investment management.

Why people hold it

• MBB Four basis points to rent the entire agency mortgage market, against a category median near 0.35%. In low-coupon bond land, that gap compounds quietly.
• Scale is the real feature: one of the largest and most actively traded funds in the mortgage-bond category, which generally shows up as tighter spreads.
• Pays monthly, and the mandate stays narrow: an index of U.S. agency mortgage-backed securities, nothing exotic bolted on.
• Among the stronger builds in a thin peer group of mortgage-bond ETFs, on the combination of cost, trading friction and issuer staying power.

• MTBA Costs 0.25% a year, below the 0.36% median for its bond-fund category. Cheap for an actively managed sleeve.
• One clear job: total return while preserving capital, per Simplify's own mandate. A specialist tool, not a repackaged broad-market index.simplify.us
• Pays monthly, has pulled in real assets since its 2023 launch, and trades with moderate volume for a niche bond fund.
• Lands in the upper half of a crowded aggregate-bond field, and its holdings line up closely with the mandate it advertises.

Worth knowing

• MBB This is one slice of the bond market. Agency mortgage paper only, with no Treasuries or corporates alongside it.
• Mortgage bonds cut both ways with rates: borrowers refinance when yields fall and sit tight when they rise, so the portfolio's duration shifts underneath you.
• On price it's a photo finish: SPMB tracks the same index at the same 0.04%, and VMBS runs a basis point cheaper.

• MTBA The index heavyweights undercut it hard: BND, SPAB and SCHZ all run at 0.03%. You are paying up for active mortgage selection.
• This is one slice of the bond market, not a diversified core. No corporates, no Treasuries ballast beyond what the mortgage sleeve holds.
• Launched in November 2023, so its track record is short by bond-fund standards and spans only one rate environment.

Full MBB profile⁠

Full MTBA profile⁠