CLIR vs SPIR vs ASTS vs FTEK

For growth investors, AST SpaceMobile, Inc.

(ASTS) is the stronger pick with 1505% revenue growth year-over-year, versus -35. 2% for Spire Global, Inc. (SPIR). Spire Global, Inc. (SPIR) offers the better valuation at 10. 0x trailing P/E, making it the more compelling value choice. Analysts rate ClearSign Technologies Corporation (CLIR) a "Buy" — based on 1 analyst ratings — the highest consensus in this comparison. The "better buy" depends entirely on your goals: growth investors should weight revenue trajectory, value investors should weight P/E and PEG, and income investors should weight dividend yield and streak.

Over the past 5 years, AST SpaceMobile, Inc.

(ASTS) delivered a total return of +688. 2%, compared to -89. 1% for ClearSign Technologies Corporation (CLIR). Over 10 years, the gap is even starker: ASTS returned +568. 8% versus CLIR's -88. 7%. Past returns do not guarantee future results, and the stock with the higher historical return may already have its best growth priced in.

By beta (market sensitivity over 5 years), Fuel Tech, Inc.

(FTEK) is the lower-risk stock at 1. 40β versus Spire Global, Inc. 's 2. 93β — meaning SPIR is approximately 109% more volatile than FTEK relative to the S&P 500. On balance sheet safety, AST SpaceMobile, Inc. (ASTS) carries a lower debt/equity ratio of 1% versus 8% for Spire Global, Inc. — giving it more financial flexibility in a downturn.

By revenue growth (latest reported year), AST SpaceMobile, Inc.

(ASTS) is pulling ahead at 1505% versus -35. 2% for Spire Global, Inc. (SPIR). On earnings-per-share growth, the picture is similar: Spire Global, Inc. grew EPS 137. 8% year-over-year, compared to -18. 1% for Fuel Tech, Inc.. Over a 3-year CAGR, CLIR leads at 80. 9% annualised revenue growth. Higher growth typically commands a higher valuation multiple — check whether the premium P/E or P/S is justified by the growth rate using the PEG ratio.

Spire Global, Inc.

(SPIR) is the more profitable company, earning 71. 7% net margin versus -482. 2% for AST SpaceMobile, Inc. — meaning it keeps 71. 7% of every revenue dollar as bottom-line profit. Operating margin tells a similar story: FTEK leads at -13. 8% versus -405. 7% for ASTS. At the gross margin level — before operating expenses — ASTS leads at 53. 4%, reflecting greater pricing power or product mix advantage. Stronger margins indicate durable pricing power, lower cost of revenue, or higher mix of software/services. They are one of the clearest signs of business quality.

None of the stocks in this comparison currently pay a material dividend.

All are effectively zero-yield and should be held for capital appreciation rather than income.

For long-horizon retirement investors, Fuel Tech, Inc.

(FTEK) is the stronger choice — it scores higher on the combination of lower volatility, dividend reliability, and long-term compounding. Spire Global, Inc. (SPIR) carries a higher beta of 2. 93 — meaning larger drawdowns in market downturns, which matters significantly when you cannot wait years for a recovery. Both have compounded well over 10 years (FTEK: -7. 8%, SPIR: -78. 8%), confirming both are viable long-term holds — but the lower-volatility option typically results in less emotional selling during corrections. Retirement portfolios generally favour predictability over maximum returns. Consult a financial advisor before making allocation decisions.

These companies operate in different sectors (CLIR (Industrials) and SPIR (Industrials) and ASTS (Technology) and FTEK (Industrials)), which means they face different economic cycles, regulatory environments, and macro sensitivities — making direct comparison nuanced.

In terms of investment character: CLIR is a small-cap high-growth stock; SPIR is a large-cap deep-value stock; ASTS is a mid-cap high-growth stock; FTEK is a small-cap quality compounder stock. These fundamental differences mean investors should not choose between them on a single metric — the "better stock" depends entirely on which of these characteristics aligns with your investment strategy.